Contents

	Page
1. Introduction	1
2. Brief geological sketch of the Cheremkhovo district	5

Geological Description of the Usolskoye Deposit

	Page
3. Tectonics	9
4. Stratigraphy:
a) Composition of the Usolskoye deposit	21
b) Position of the Usolskoye Paleozoic in the general stratigraphic scheme of the Irkutsk Amphitheatre	39
5. Groundwaters and springs	42
6. Water regime of the wells and boreholes of the Usolskoye deposit	47
7. Conclusion	52
8. Appendices	56
9. List of cited literature	69
10. Description of figures	70

M. K. Korovin, Prof., STI.

The Usolskoye Rock Salt Deposit in Irkutsk Governorate

Introduction.

The Usolskoye salt deposit, which supplies the Irkutsk saltworks and the Usolskoye resort, is located near the town of Usolye, 60 versts to the northwest of the city of Irkutsk and 3 versts from the Angara station of the Trans-Baikal Railway. It was discovered, probably as early as the seventeenth century, by Yenisei Cossacks ascending the Angara River. In any case, already in 1703 an Irkutsk resident, Ignatii Iurinskii, had set up salt boiling here. But he sold the salt at “a high price, 5 altyns and 2 dengas,” and, upon the petition of “Irkutsk service people,” in 1704 the salt industry was transferred to the Irkutsk Ascension Monastery (43)¹. At the end of the eighteenth century the industry passed into the jurisdiction of the treasury, and at the beginning of the nineteenth century it was transferred to the mining department, being subordinated in the 1830s of that same century to the nearest supervision of the Governor-General of Eastern Siberia (44). What the strength of the brines was at that time, and on what scale the works operated, no information has survived. It is known only that the brines were obtained from wells sunk at the sites of natural outlets of salt springs. From 1823 the salt industry already appears under the name of the “Irkutsk Saltworks” (2). In the 1860s (44) eleven boiling pans were in operation there, and the annual production of common salt reached 275,000 poods. At that time the works already supplied salt to Irkutsk Governorate, part of Yenisei Governorate, and Trans-Baikal Oblast (44).

From approximately the same time attempts began to study the deposit and to exploit it more rationally (45). Thus, in the period from 1877 to 1880 a deep borehole was drilled on Varninyi Island by engineer Brodovich, under whose name it is still known today (Fig. 3). The borehole did not encounter the strong brine expected, and at a depth of 190 m it was stopped. Nevertheless, Brodovich’s borehole was exploited by the works until very recent times. The strength of its brine is 9° B.

In 1895, the manager of the works, engineer A. I. Sosov, sank three shafts on the left bank of the Angara River, opposite the pontoon bridge, in order to study the composition of the rocks above the level of the Angara River. The shafts encountered Jurassic sandy-clayey deposits with thin interbeds of coal. And at the level of the Angara River, Paleozoic limestone underlying the Jurassic was established.

In 1898, engineer Voislav began drilling the so-called “Diamond” borehole in the resort park (Fig. 4), with the aim of finding strong natural brine. Drilling continued until 1904. The borehole did not encounter strong brine, and therefore was stopped at a depth of 360 m. The borehole still flows weakly to the present day, yielding brine of 5° B strength.

In 1899, mining engineer A. I. Sosov carried out exploration by shallow drilling on Spasskii Island (Fig. 4), with the aim of finding industrial coal seams. Five boreholes were drilled, from 12 to 25 m deep; of these, one was on the left slope of the Angara River, in the yard of the works’ office. In two boreholes

exploration encountered coal seams more than 1 m thick. In all the boreholes the saline brine proved to be of low strength. The boreholes did not reach the Paleozoic limestones.

In 1901, Engineer Pedashenko, with the participation of the geologist of the Irkutsk Mining Administration Ryazanov, carried out exploration for coal on the left side of the Angara River, northwest of the plant. Precise data on this exploration have not been preserved. It is known only that it did not find industrial coal seams.

In 1911, by order and at the expense of the Irkutsk Mining Administration, Engineer Mukhin carried out exploration for coal in the vicinity of Angara station; this likewise yielded no positive results.

In 1912, in the Mining Department there arose the idea of transferring the salt-boiling plant to Malta station (Fig. 1) and of exploring the vicinity of this station by deep drilling. The project of transferring the plant from the town of Usolye remained unrealized, but the borehole was nevertheless sunk to a depth of 470 m, without encountering strong brine.

In 1915, A. I. Sosov conducted new drilling exploration on Spassky Island, with the aim of finding brine both for the salt-boiling plant, which, in view of the expected increase in its productivity, proposed to transfer part of its installations here, and for the health resort, which also wished to move to this island. Four boreholes were sunk, and one in the upper part of Varnichny Island, the greatest depth of the boreholes being 40 m. In all the boreholes, which were sunk through Jurassic deposits, brine of low strength was found.

In the period from 1916 to 1922, in view of the expansion of the plant’s productivity, which had already reached almost 1 million poods per year (39), three deep boreholes, Nos. 1, 2, and 3, were laid down on Varnichny Island to find strong brines. But, for lack of the necessary materials, none of them was brought to the intended depth: No. 1 stopped at a depth of 664 m, No. 2 at 478 m, and No. 3 at 420 m. At the depths reached by all three boreholes, brine of high strength was not found: it remained within the former limits of 5° to 9° B. Throughout their entire depth the boreholes passed through a Paleozoic mass of limestones with insignificant, chiefly clayey interbeds.

Subsequently it proved possible to continue only one of the named boreholes, No. 1, which in January 1923, at a depth of 693 m, cut into a bed of rock salt that continued down to a depth of 722 m, where drilling, owing to the breakage of the steel cable, was again suspended. The brine at the depth of the salt bed reached a strength of 25° B. (1).

In connection with the gradual development of the salt-boiling plant and the natural revival of the town of Usolye (then a village), there arose also the Usolye health resort. Its discovery is assigned to the year 1875, when on the left bank of the Angara River, opposite Varnichny Island, at the place where brine springs emerged onto the surface of the alluvium, after these had been captured, a small log building of the resort was constructed, with primitive devices for pumping and heating the brine. In 1902, on the same site, a new, fairly extensive and more or less equipped resort building arose, around which a small park was laid out that same year (46; 10, 23). From the very moment of its emergence the resort was one of the enterprises of the salt-boiling plant, and only after the revolution did it pass under the jurisdiction of the resort administration. It is therefore understandable that during all this time no special investigations were carried out here either of the composition or of the nature of the brine: the study of the deposit was determined by the demands presented to it by the salt-boiling plant.

It must, however, be said that all the above-listed, generally quite large, exploration works conducted in the area of the Usolye deposit were fortuitous in character: there was no worked-out plan of exploration, nor could there have been one, since it would have had to be based on a special geological survey of the deposit area, which likewise pro-

was not introduced. The work carried out should nevertheless have accumulated considerable geological material illuminating the deposit; but in this respect matters stood very poorly. The drilling even of deep boreholes was carried out without proper geological supervision; consequently, there could be no adequate geological documentation of the drilling data obtained, which, naturally, gave no answer to a whole series of fundamental questions of the geology of the deposit, being limited only to the search for strong brines. The reason for all this lies in the extremely limited funds allocated for exploration, and it is only owing to the individual interest in studying the deposit on the part of the last manager of the plant, mining engineer A. I. Sosov, that we are indebted for the small amount of material that has survived to the present in the form of drilling logs, sections, and rock samples.

After what has been said, the difficulties encountered by individual investigators who in one way or another had to deal with the question of the Usolskoye deposit become understandable. The state of the data from many years of exploration work characterized above always forced them either to confine themselves to indications on individual questions, or to the most general propositions concerning the geology of the deposit. Hence it is also understandable that the fairly extensive literature on the Usolskoye district, accumulated over more than a century of the saltworks’ existence, is rather poor in geological content, not illuminating even the fundamental questions of the geology of the deposit. The greater part of the articles and notes relating to the plant most often concerns only questions of its equipment, the conditions and technique of concentrating the weak brines with which the plant was supplied until 1923, the composition of the brine and of the salt obtained, and the conditions of marketing the latter in the markets of Eastern Siberia. Such, for example, is a series of the following articles that appeared in the Mining Journal from the beginning of the nineteenth century.

1. “Description of the Irkutsk Saltworks and its operation, established in 1823” (2; 83). The annual productivity of the plant is indicated: before 1823 it amounted to 160 thousand poods; from 1823, 210 thousand poods.

2. “On the operation of the Siberian saltworks in 1840” (3; 343). An increase in productivity to 240 thousand poods per year is noted.

3. F. Lvov. “Report on activities at the Irkutsk Saltworks” (4; 478). In addition to a description of the equipment and operation of the plant, the report gives a number of analyses of brine and salt, as well as brief information on the environs of the plant, in particular on the valley of the Usolka River, where remnants of salt making in the eighteenth century were found.

4. Stemnilevsky, mining engineer. “The salt industries of Eastern Siberia” (5; 227). The author, assigned to study the salt industries of Siberia on site, provides a number of interesting facts also concerning the Usolskoye deposit. For example, according to information he obtained from the old residents of Usolye, he reports that in former times the strength of the spring brines reached 18°. But after the earthquake it suddenly fell to 12°. Verification of these data against archival documents showed only that in the period from 1866 to 1875 the strength of the brines fluctuated between 5.5° and 10° according to Lambert. It was not possible to obtain information for an earlier time in the archives, since all archival files perished during the great fire in Irkutsk. Also of interest is the report that in spring, during the high-water stage in the Angara, the brines increase in strength by \(3/4^\circ\), and after the fall of the water they decrease to the normal level¹.

Of much greater significance for elucidating the geology of the deposit was a series of major works on the geological survey of Irkutsk Governorate, carried out in the last quarter of the nineteenth century. These were, above all, the works of the foremost investigators of Siberia A. Chekanovsky (6) and I. D. Chersky

(7; 8), which still belong to the seventies and eighties of the past century, but which for the first time placed the geological study of Irkutsk Governorate on firm scientific foundations. In particular, Chersky is credited with establishing the Paleozoic age of the red-colored strata of Irkutsk Governorate, with which the outlets of saline springs in it are associated. In the Usolye region he allowed for the possibility of significant tectonic disturbances, with which the valley of the Angara River itself is connected here (8).

In 1892 a new major work appeared, by Prof. V. A. Obruchev, on the Early Paleozoic sedimentary rocks of the valley of the Lena River between the Kachug and Vitim stations (9). This work gives a detailed description of the Paleozoic of the upper Lena system, and brings all the factual material into a coherent stratigraphic system of the Paleozoic of Irkutsk Governorate.

In 1896, in connection with the construction of the Siberian Railway, a major work by K. I. Bogdanovich was published, “Materials on the Geology and Mineral Resources of Irkutsk Governorate” (10), which gives a detailed geological description of the southern part of Irkutsk Governorate, with clarification of the composition, tectonics, and mineral resources both of the coal-bearing strata of the mountains and of the Paleozoic formations. Relying on the investigations of Obruchev, Bogdanovich comes to the conclusion that the salinity of Usolye is connected with the lower red-colored strata of Irkutsk Governorate, namely with the suite of Moty red sandstones (10; 202). The salt brines, however, come out onto the surface along tectonic fissures oriented at an azimuth of 15°–20°.

Of some interest, too, is a series of works on determining the coal-bearing character of the crust in the Usolye region, dating from the middle of the nineteenth century.

It appears that the first explorations for coal date as far back as 1834, when, according to A. Keppen, in the vicinity of the plant a coal seam 9 ft. thick was found (11). In 1852 exploration was carried out on the right bank of the Angara River, in the Kurganikha hollow. But it did not yield positive results (12; 213). In 1853 the plant manager Yakhimovich discovered a coal seam in the valley of the Maltyanka brook (12; 213). Exploration was continued there by the plant manager Kozlov, who in 1854 discovered a seam 1.5 arshins thick and determined coal reserves of up to 1 million poods (12; 214). In 1855 and 1856 exploration was conducted by Lieutenant Colonel Tashkin, who discovered in the vicinity of the plant a coal deposit with reserves of 2.4 million poods; but the location of this deposit remained unknown (12; 214).

Among later investigations in this direction, in addition to those mentioned above, one must also name the work of Prof. V. A. Obruchev on brown-coal deposits in Irkutsk Governorate, which appeared in 1891 and gives a list of all known coal outcrops and a bibliography on the geology of Irkutsk Governorate (13), as well as the above-mentioned work of K. I. Bogdanovich (10).

Exploration for coal did not cease in the subsequent period up to 1905, when mining engineer A. I. Sosov discovered and explored a coal deposit on the right bank of the Angara River near the village of Barkhatova, directly opposite the town of Usolye. From 1906 exploitation of this deposit had already begun (46; 24).

With the beginning of the twentieth century there was a gradual expansion in Irkutsk Governorate of the work of the Geological Committee, which was of great importance for contemporary conceptions of the geology of this governorate. On the Angara River, at the Padun rapid, A. Rzhosnitsky carried out investigations; in the system of the Vikhlya River and in the upper reaches of the Kirenga River—P. I. Preobrazhensky, A. Rzhosnitsky, and S. F. Malyavkin; in the lower reaches of the Irkut River—G. Frederiks; in the region of the western Baikal area—M. Tetyaev and Svitalsky (14; 15; 16; 17; 18).

From 1919, first by the Siberian Branch of the Geological Committee, and then, from 1923, by the Central Geological Committee, in the southern part of

in Irkutsk Governorate, within the limits of the Irkutsk coal basin, systematic geological investigations began, also covering the area of the Usolskoye deposit, and continuing up to the present time. The results of these works have been published only in part. One may mention the reports of M. K. Korovin on the geology of the Cheremkhovo coal district and on route investigations along the B. Belaya River, as well as the report of M. M. Tetyaev on investigations in the foothills of the Eastern Sayan and of Yu. A. Zhemchuzhnikov in the valley of the Angara River, in which new elements of the stratigraphy and tectonics of the coal-bearing crust and the Paleozoic are clarified (19; 20; 21; 32).

All the investigations and works enumerated have gradually led to the establishment of the age of the Irkutsk Paleozoic and to the development of its stratigraphy, adopted in the present article. Their results have found expression also in a number of recent summaries, among which special mention should be made of the major work of Prof. V. A. Obruchev, Geologie von Sibirien (40).

To what has been said about the history of the study of the Usolskoye salt deposit, a few more words must be added about the characteristic features of the very latest period. In 1924–25, after the discovery in borehole No. 1 of a thick bed of rock salt, a new phase began in the history of development and study. The Irkutsk saltworks began to exploit from this borehole an artificial brine of high strength by means of the compression method, and new economic prospects opened before it (1): the Usolskoye deposit acquired regional significance, and in the five-year work plan developed by the Siberian regional organs of the mining industry, an output of up to five million poods of salt per year was projected for the plant, with the possibility of further expansion of production. In connection with this, the gubernia organs of Gosplan allotted special credits for the further prospecting and study of the Usolskoye deposit. In 1925 the deepening of the unfinished borehole No. 3 began, and in the summer of the same year, on the initiative of the Assistant Head of the Siberian Mining Supervision, mining engineer K. N. Tulchinsky, and with funds from the Irkutsk Gubernia Department of Local Economy, the author of the present article carried out a geological expert examination with a survey of the district of the deposit, with small prospecting works in the form of a series of ditches, pits, and shallow boreholes, and with a special topographic survey of the environs at a scale of 100 sazhens to the inch (Fig. 4).

As a result of these works, carried out with the assistance of mining technician K. D. Egorov and topographer K. P. Kolesnikov, as well as of the study of archival materials with the cooperation of the head of the East-Siberian Bureau of Accounting, F. F. Shvaid, the following description of the geology of the area of the Usolskoye deposit has been made.¹

Brief geological outline of the Cheremkhovo district

The study of every deposit of a useful mineral must be based on the geology of the district of which it forms a part, as a part of an organic whole. This must be said especially of the Usolskoye deposit, which lies at a depth of more than seven hundred meters and therefore requires clarification of the geological structure of a considerable segment of the earth’s crust. From the latter point of view, in the geology of our deposit some aspects still remain unclear, since systematic geological investigations in Irkutsk Governorate have covered chiefly the area of the Irkutsk coal basin, and the stratigraphy of the series of Eopaleozoic rocks, underlying

coal-bearing deposits, which have as yet been insufficiently studied¹). Nevertheless, these investigations cover a fairly extensive area, and on the basis of the results obtained by them and the whole sum of the geological materials that have accumulated, the fundamental questions of the geology of the Usolskoye deposit can be resolved satisfactorily.

The region of the town of Usolye, with the Irkutsk salt-boiling works, is situated on the southeastern margin of the central part of the Irkutsk coal-bearing basin and, in its geological structure, is so closely connected with it that it is necessary first of all to dwell on the main features of the geology of this part of the basin. Since in this part of the Irkutsk basin are located the Cheremkhovo mines, in what follows we shall call it the Cheremkhovo district.

As over the entire area of the basin, in the Cheremkhovo district (fig. No. 1) two most important formations are developed: the coal-bearing Jurassic on the one hand and the ancient Paleozoic underlying it on the other²). The Jurassic deposits form a series of small areas, often isolated from one another, and are distinguished by a very small thickness, usually not exceeding 20–30 meters. But as one goes away from the Cheremkhovo mines to the NW, toward the system of the Zalari River, and to the SW, toward the city of Irkutsk, as well as to the SE, toward the valley of the Belaya River, the separate islands of Jurassic become connected, and its thickness increases from 20–30 meters to 100 meters and more.

The indicated peculiarity of the distribution of the coal-bearing Jurassic deposits in the Cheremkhovo district finds its explanation in the main features of the tectonics of this district, which consist in the fact that here two very gentle, but fairly broad, anticlinal uplifts converge. One has a northwestern direction (NW: 320°), coinciding approximately with the direction of the line of the Tomsk Railway, and is known as the Bulai anticline; the other—the northeastern (NE: 60°)—from the village of Belsk on the B. Belaya River crosses the railway line and then passes through the valley of the Angara River at the settlements of Buret, Barkhatovo, and Svirskaya, and is called the Buret-Belsk anticline. The mutual intersection of the named anticlines entails the formation, in the Cheremkhovo district, of a brachyanticline or dome, dipping in all directions. To this dome are due the insular character and small thickness of the coal-bearing Jurassic, which in considerable part has already been washed away by erosion in the area of its maximum uplift, but with increasing distance from the latter forms a more or less continuous coal-bearing field and reaches considerable thickness. The same dome-like uplift of the rocks and the subsequent irregular manifestation of denudation account for the wide development of Eopaleozoic limestones in the central part of the district and their gradual subsidence, with covering by the coal-bearing Jurassic, toward the periphery.

The two anticlines named above also find expression in the region of the Usolskoye deposit, which lies on the southeastern wing of the NE Buret-Belsk anticline and on the northeastern wing of the northwestern Bulai anticline. For elucidating the geology of the Usolye district, the first of the named anticlines is of greatest importance, and it is therefore necessary to discuss it in greater detail.

In figs. 5 and 6 are given schematic sections of the southeastern wing of this anticline along the valleys of the Belaya and Angara rivers. It may be characterized by the following features. After a fairly high uplift of the Eopaleozoic limestones to an elevation of up to 150 meters above the level of the Angara River in the Buret-Barkhatovo sector, the upper hypsometric boundary of this formation slowly descends downward, and at the village of Olonki finally disappears beneath the level of the river, being replaced upward along the section by Jurassic deposits. The subsiding

¹) The results of the work of the geologist M. M. Tetyaev, who has recently carried out investigations in the foothills of the East Sayan, where the Eopaleozoic formations are most fully represented, have not yet been published.

²) On the geological map, fig. 1, the most recent Quaternary deposits are not shown.

on the SW limb of the fold it thereby forms a system of folds of the second order, but the height of the anticlinal uplifts above the river level gradually decreases. In connection with this, the sandy-clayey Jurassic sequence, which appears in the bank bluffs at first only in synclinal depressions, above the village of Ponomareva already forms a continuous light-yellow band, subject to the same gentle undulation, while upstream from the village of Olonki it makes up the entire right slope of the Angara River. Folding of the second order is characterized, moreover, by a consistent tectonic type and is represented in most cases by oblique folds, with a long and very gently dipping limb facing NW, and a short limb, more steeply inclined to the SE. This feature of the second-order folding is very clearly observed both along the Belaya River—for example, in the Kholmushina—Ust-Chernaya section (Fig. 6)—and along the Angara River, for example, in the Ponomareva—Olonki section (Fig. 7).

The right slope of the Belaya River below the village of Kholmushina reveals, at first sight, an apparent discordance between the relief and the tectonic structure of the area (Fig. 6): whereas the watershed line of the slope clearly descends downstream, a fairly large number of outcrops of Paleozoic limestones usually show a dip direction to the NW, i.e., upstream. But a more attentive examination of a series of such exposures shows that a system of small anticlinal folds is developed here, distinguished by rather long and calmly lying upper (downstream) limbs, gently dipping to the NW, and comparatively short lower limbs, rather steeply dipping to the SE, often tectonically crumpled and disrupted. Evidently, before us here is a series of one-sided folds with crumpled and fractured, sometimes torn by upthrusts, southeastern limbs, as is shown in Fig. 6a. The shattered southeastern limbs of the folds naturally are rapidly destroyed, being masked by talus; but the very gentle upper limbs give a series of significant exposures, which at first sight appear as a homoclinal series of beds dipping concordantly to the NW.

The same type of disturbance is also observed along the Angara River. In Fig. 7 a normal section of the right slope of the Angara River in the Ponomareva—Olonki area is constructed, showing the limestone outcrops occurring here and their disturbances. Over a distance of about 6 km, a series of folds more or less shifted to the SE is observed here, the anticlinal closures of which gradually lower toward the river level upstream. At the Ponomareva flexure¹ the limestones rise to a height of up to 50 m; near the village of Ponomareva their upper hypsometric boundary is no higher than 30 m; opposite the mouth of the Belaya River it descends to a height of 20–25 m; and at the village of Olonki it reaches 5–10 m above river level. As along the Belaya River, the limestone outcrops are often masked by talus—which is especially often observed in synclinal depressions, almost always coinciding with large or small ravines and gullies, and also on the limbs of folds dipping to the SE, which are exposed comparatively rarely. The more frequently observed anticlinal folds are almost always characterized by gently dipping NW limbs, the angle of inclination of which does not exceed 8°–12°. In these limbs of the folds, no other manifestations of tectonic deformation of the beds are ever observed. The SE limbs of the same folds, more rarely preserved from destruction, are always distinguished by a steeper inclination to the horizon, the angle of which, however, in most cases is not great here either, usually not exceeding 20°–35°, and only in rare cases reaching 85°–90°. Thus, here too, minor disturbances of the type of oblique folds predominate, and only occasionally do areas appear that have been deformed on a larger scale, such as the Ponomareva flexure, where the depth of subsidence of the beds may reach as much as 100 m. However, even under conditions of small and gentle folding—

¹ 0.5 km above the village of Ponomareva.

The section of the Angara River under consideration often reveals signs of disruptions of a different order, in the form of bands of crumpled and ground-up rocks, which could have formed only under conditions of disjunctive displacement of the strata, for example along upthrow-fault fractures. Such bands of crumpling always find clear expression in the upper Paleozoic horizons, where the weakest member of this formation is developed, in the form of an easily crushed breccia-like conglomerate. And the best indication of such displacements is the characteristic fragments of breccia-like conglomerate with polished surfaces, scattered over the slopes. A large number of such indications is observed in the immediate vicinity of the lower part of the village of Olonki, where there is a series of small and gentle folds and, among them, at least two or even three upthrow-fault fractures.

We also find a typical expression of these disturbances in the lower course of the B. Belaya River, at the crest of the Malta bend, near the locality of Klyuchi (Fig. 8). Here there appears a series of crumpled folds, observed along the right bank of the river for a distance of up to four hundred meters. Fig. 8 shows the natural outcrops of the rocks at the crest of the Malta bend, with an indication of the conditions of their occurrence, and a possible reconstruction of the disturbances, outlining one upthrow fault and a series of minor disturbances of the overthrust type (22; 29), which caused strong grinding of the breccia-like conglomerate along the fracture planes. The crumpled zones of rocks here, too, are always associated with the southeastern limbs of the folds. In the clearly outlined upthrow fault of this disturbance, attention is also drawn to the shell-like character of the fault-plane surface, steeply set in the frontal part and rapidly passing into a horizontal position, with a conformable displacement at the hinge (22; 28) of the disturbance. Such an orientation of the fault-plane surface is evidently very characteristic of our area, since in a number of cases it has also been recorded at the Cheremkhovo mines (19; figs. 17–19). However, the understandable crumpling and crushing of the rocks participating in such disturbances entails rapid weathering and their covering by talus and even vegetation, which is the reason for the comparatively rare preservation of these tectonic forms in the Irkutsk coal basin.

To the above brief description of tectonic disturbances it is necessary to add a characterization of the deformations associated with them in the rocks. Here it is necessary first of all to point out the formation of often numerous and variously oriented, sometimes regular and sometimes irregularly curved, as it were worm-like, always small fractures, most often filled with silica, calcite, and chalcedony, more rarely with pyrite. Very widespread are entire zones of crumpling, which accompany many disturbances and are expressed by the development of compressed thin-platy, often even schistose limestones, and sometimes typical tectonites in the form of almost black clay shales, forming a selvage along the surface of displacement. On the hanging wall of displacement fractures there are also developed, often attaining considerable thickness, various tectonoclasts, such as broken and destroyed limestones and limestone rubble cemented with clay, and especially breccia-like conglomerate, weakly cemented by a finely ground mica-like aggregate of pelite. Cellular and spongy limestones are also very widespread, the cavities of these rocks, like the fractures mentioned above, very often being filled with iron oxides in the form of ocher or brown iron ore, gypsum, or calcite. The latter shows that an energetic circulation of groundwater is always associated with tectonic fractures and zones of crumpling. We have an example of this both in the Ponomarevo flexure, where a large number of thin siliceous veinlets is observed, and in the band of disturbances above the village of Olonki, where, together with ground-up breccia-like conglomerate, there is developed a horizon with gypsum and ocher, reaching in places a thickness of 60 cm.

The strike of the folds, flexures, and associated reverse faults described above varies within the limits of azimuths: 35°—60° and, on average, may be taken as NE: 50°, which occurs more often than the others.

Everything said above about the Cheremkhovo district gives us grounds for separating from it, in tectonic terms, its southeastern margin and characterizing it as an area of rather significant disturbances, with numerous folds—although in most cases gentle, but often strongly crumpled—which not infrequently give rise to reverse-fault fissures. In addition, the preservation of the indicated features of the tectonic structure in the valley sectors of the Angara and B. Belaya rivers, connected with one another by a NE azimuth, permits the supposition that the largest zones of disturbances here persist over a broad area, and at the same time permits the most important lines of disturbance to be marked on the geological map, Fig. 1, according to the above-mentioned mean NE azimuth: 50°. These tectonic lines already provide some explanation for many facts connected with the history of the Irkutsk saltworks.

Thus, in the vicinity of Mal’ta Station and the village of Taiturka, salt springs and salt marshes have long been known, occurring along the Mal’tinka River and the Usol’e River. One of these salt marshes is situated on the left side of the B. Belaya River, between the village of Taiturka and the railway line, at the mouth of the Balagan Pad’. Here a shallow pit was sunk, which encountered saline water. And at a short distance from this point, salt springs were discovered in the very channel of the Belaya River when deepening the excavation for the abutment of a railway bridge, (47). On the geological map it is evident that the salt marshes and outlets of salt springs of the village of Taiturka are connected with the tectonic belt of disturbances of the Ponomarev flexure.

Directly below the village of Taiturka, on the right side, the small Usolka River flows into the B. Belaya River; with it there is likewise associated a series of data on salt marshes and salt springs, especially developed in the upper course of the named river, where even the remains of an old saltworks were found. And in 1912, in connection with the question of building a new saltworks in Usol’e, the Mining Department conceived the idea of transferring this works to Mal’ta Station, and a borehole was drilled in the headwaters of the Usolka River, at a distance of about 3 versts from this station (23). On the geological map, Fig. 1, the headwaters of the Usolka River are cut by a new belt of disturbances, outlined on the basis of a series of folds and reverse-fault displacements in the region of the upper limb of the Balai bend of the B. Belaya River, in the sector between the former Tikhomirov works and the settlement of Balai.

In the vicinity of the same Mal’ta Station, through the lower course of the Mal’tinka River, there passes yet another belt of disturbances, running from the above-described system of folds and reverse faults at the crest of the Mal’ta bend. To the NE it crosses the Angara River with a series of crumpled folds below the village of Olonok, and to the SW it goes through the lower reaches of the Mal’tinka River, where salt marshes and a well with saline water are also known.

The belts of tectonic disturbances enumerated above include, in each particular case, entire systems of crumpled zones, folds, and reverse faults, and owe their origin to a pre-Jurassic and partly post-Jurassic, probably Cretaceous, phase of folding, since Jurassic deposits always take part in it as well.

GEOLOGICAL DESCRIPTION OF THE AREA OF THE USOLSKOYE DEPOSIT.

Tectonics.

The brief geological sketch of the Cheremkhovo district given above, reduced chiefly to a review of its tectonic structure, brings us to the geology of the Usolskoye deposit, since here too the principal element is tectonics, in which questions concerning ...

of the underground circulation of waters, the ascending flows of saline brines, and their emergence at the daylight surface in the form of salt springs, i.e., those questions with which the entire history of the Irkutsk salt works is connected.

The general scheme of the structure of this deposit, after what has been set forth, appears to us very simple, since the Usolye district constitutes a normal segment of the same southeastern limb of the Buret–Belaya anticline, repeating all those features of its structure that have been briefly described above. For elucidating these features, the most instructive is the left bank of the Angara River, near which both the salt works and the Usolye resort are situated. As for the right slope, here, as in other parts of the upper course of this river, it attains a rather considerable height, up to 70 meters and more, is often fairly steep, and is rich in natural exposures of rocks; in this respect it is of great interest to the investigator. But it is composed entirely of Jurassic deposits, in many horizons diagenetically rather weakly consolidated, and in surface exposures almost or even entirely loose, and therefore it is little favorable for the study of tectonics: even the weakest tectonic disturbances in Jurassic rocks are almost always masked by talus and, quickly becoming covered with vegetation, are wholly inaccessible for study. Hence, in clarifying the tectonics of each sector in the Irkutsk coal basin, one inevitably has to turn to the Paleozoic, which in the environs of the town of Usolye is developed only on the left slope of the Angara River. This slope in most cases is very gentle and is distinguished by small heights, rarely exceeding 10–15 m above the level of the river. Nevertheless, it has a series of natural exposures of rocks, exposing above the resort and the salt works exclusively Jurassic deposits, and lower down the valley, chiefly Paleozoic limestones, which, in connection with the data of old prospecting and the small exploratory works of 1925, provide factual material sufficient for constructing a series of longitudinal and transverse sections of the deposit.

In Fig. 9 a longitudinal section of this slope is shown, giving a general idea of the tectonic structure of the deposit area. The section covers the segment of the valley from Zaimka Zaitsev to the village of Malta (Fig. 2), which may be characterized as follows¹.

At the extreme lower point of the section, at Zaimka Nechaeva, there is evidently a synclinal fold, since the limestones, below and above the zaimka reaching in outcrops a height of 10–15 m, near the zaimka suddenly disappear, and their place at the river-bank bluff is taken by a Jurassic clayey conglomerate interbedded with weathered argillite, yielding a good refractory clay, developed up to the horizon of the meadow terrace. In the refractory clay a preserved prospecting pit had been sunk, which established its continuation to depth, but because of a strong inflow of water did not reach the bedrock floor. The thickness of clay exposed at the pit dips to the NW 300° at an angle of 20°–25°². Above Zaimka Nechaeva the limestones rise rather rapidly above the river valley and over a considerable distance lie almost completely undisturbed, only in places revealing a slight dip to the SE or NW. Thus, opposite the upper part of Listvenichny Island (Fig. 2) the limestones dip at an angle of only 4° to the southeast; and two versts higher, with the same magnitude of dip, they dip to the NW and have a strike of NE 60°. The direction of dip of the rocks changes somewhat

but more often a dip toward the southeast is observed, and this continues as far as the small island in the Angara River opposite the village of Zaitsevo, where the rocks dip to the SE at an angle of 4°. For about 3 km from the village of Nechaevo to the village of Zaitsevo there is thus an almost continuous outcrop of limestones rising above the river valley to a height of up to 5–15 m, corresponding to a very gentle anticlinal uplift, which may be called the Zaitsevo anticline.

The replacement of the above-mentioned Nechaevo syncline by an anticlinal uplift also entails a noticeable change in the relief of the locality, both in the vertical and in the horizontal plane. The Nechaevo syncline, with the limestones sinking below the level of the Angara River, produces a strong lowering of the slope, and, owing to the development above the submerged limestones of weak Jurassic clays and pebbles, the valley here forms, moreover, a rather deep bay (Fig. 2). Conversely, the small Zaitsevo anticline, causing an uplift of the slope, is accompanied at the same time by a noticeable advance of it toward the valley. A genetic connection with tectonics, as was noted above for the Cheremkhovo district, can be discerned even in small elements of the relief. For example, in the middle part of the same Zaitsevo anticline there is observed a noticeable depression of the second order, and it may be attributed to small folds or even minor faults, as may be indicated by the springs of groundwater developed here. But in the features of the vertical dissection of the left slope of the valley, along with this, the lithological composition of the underlying formations is also reflected. Thus, the formation in many places of the valley of a narrow meadow terrace, with a low ledge of the left slope receding into the interior of the mainland, is often due to the development within the limestones of two varieties of this rock: the meadow terrace, rising above the level of the Angara River by only 1–2 m, is usually composed of more or less massive gray limestones, while the ledge receding into the slope, rising above the terrace by 8–12 m, is always composed of platy marly limestones of gray and light-gray color, to which the large number of lime-burning kilns and quarries operating here is due.

Immediately above the village of Zaitsevo the left slope of the Angara River, in accordance with the indicated SE dip of the rocks, again becomes strongly lower; the limestones disappear completely; in rare small bluffs and ravines there appears sandy-pebbly deluvium of the mountain, and, in accordance with the new geological conditions, the slope of the valley retreats far to the west under the pressure of the waters of the Angara, which rapidly erode the loose Jurassic thickness. Here we have, probably, a second syncline, which may be called the Berezovy syncline, since opposite it lies Berezovy Island.

Opposite the upper half of the same Berezovy Island the limestones again rise from beneath the level of the river and, maintaining themselves at a height of about 8–10 m for a distance of up to 1.5 km, form the so-called Limestone Cape, which projects rather sharply into the valley of the Angara River (Fig. 2). In the lower part of this cape, where it rises highest, there is a large quarry, in which the rocks have a strike NE:20°, with an eastward dip at an angle of about 10°. There too are recorded the directions of joints and bedding surfaces: NW:300°, with vertically oriented joints, NE:22°, with the joints dipping westward at an angle of 60°, and the meridional direction, rarely observed in the district. Good outcrops of limestone are provided by the quarries of the upper, lower half of the cape, where they have a strike NE:70°, with a dip angle to the SE of 6°, and bedding joints oriented most often along azimuths NE:50° and NW:320°. Occasionally, here too, bedding joints of azimuths NE:25° and NW:300° are observed. The limestones of the cape are represented by the same varieties of rock: at the base of the slope massive ...

clayey, and in the upper half—marly and thin-platy. But, owing to the probable development here of second-order folding, these rocks do not exert any appreciable influence on the vertical distribution of the dip.

At the channel between Berezovy and Spassky Islands (Fig. 2), Izvestkovy Cape, in accordance with the dip of the rocks to the SE, gradually lowers; the slope of the valley retreats far back, forming a meadowy and, in places, marshy terrace up to 150 m wide, and the limestones, having sunk below the level of the Angara River, again give way to sandy-shaly and clayey Jurassic deposits. After the anticline of Izvestkovy Cape we have here, evidently, a new synclinal depression, which should be called Varnichny, since directly opposite it, beyond the narrow channel of the Angara River, lies Varnichny Island and on it the saltworks. The depression of the Varnichny syncline, complicated—judging by the relief¹—by small folds of the second order, as was confirmed by the data of ditches and trial pits in 1925, continues for about 1 km, to the middle part of the park of the Usolye resort, where, at a height of about 6 m above the level of the river, there is an interesting outcrop of limestones with a clearly expressed fault, striking NE:50°. This outcrop corresponds to the small “Resort” anticline, beyond which follows the compressed but rather deep “Almaznaya” syncline, since the diamond borehole of Voislav was laid on it and encountered Paleozoic limestones at a depth of 34 meters. At a distance of about 200 meters from the Resort anticline there occurs an anticline of the same type, the crumpled “pontoon anticline” (near the pontoon bridge), which is weakly reflected in the local relief, but was established by a series of resort buildings and by the exploration of mining engineer A. I. Sesov in 1895 (45), which encountered limestones at the very level of the Angara River. On the basis of the data from deep drilling on Varnichny Island, it may be considered quite probable that this anticline too is broken by fault fissures. Direct observations of the outcrops of limestones with a well-preserved fault in the Resort anticline, as well as the orientation of the tectonic fissure with the outlets of salt springs cutting through the Angara channel immediately above the pontoon, show that the axes of the named folds have a strike close to an azimuth of NE:50°.

Above the saltworks and the resort park, the Paleozoic limestones already plunge to a rather great depth, and the tectonic structure of the area situated higher along the Angara River has to be judged from the outcrops of Jurassic rocks, taking into account also the character of the relief, which, as is evident from the preceding, is always connected in our region with tectonics. But because of the already indicated features of the weak and easily destroyed Jurassic rocks, the details of the structure of this part of the section are not available to us, and we can judge only its principal features, which amount to the following.

The depth of submergence of the Paleozoic above the resort rather quickly reaches values up to 40 m, as is evident from the data of the 1915 exploration on Spassky Island (45). These new conditions of occurrence of the Paleozoic, without any noticeable fluctuations, continue over a stretch about 1.5 km long, which may be called the Yamanya syncline, since it lies opposite Yamany Island. Near the match factory, the smoothed and lowered slope of the Angara River, which had receded before this, again approaches the modern channel, forming a small cape corresponding to the beginning of the probable anticline here of Spassky Island. The cape has a small height, up to 8 m above the river level, and is composed of Jurassic rocks gently dipping to the WSW at an angle of 11°, and broken by

by two systems of joint cracks with strikes NW:300° and NE:10°—15°. Immediately in front of the cape and above it there emerge fairly strong springs of fresh water. The anticline of Spassky Island, judging by the rather persistent character of the slope, which remains within the same elevation and close to the river channel, continues upward for at least 1.5 km, giving a series of Jurassic exposures. The most interesting exposure is in the middle part of this distance, where the Jurassic sandstones have a strike NW:320° and dip to the SW at an angle of 15°—17°. The same sandstones show very clearly expressed joint cracks with a strike NE:45°—50°. Near this exposure there issues a spring of artesian, slightly saline water. The latter point coincides with a small probable lowering of the anticline, after which it again slowly rises, reaching a maximum of uplift before the broad Telmin bog, 1.5 km below the village of Telma. The left slope of the Angara River here approaches the channel itself, reaches a height of 15 m, is very steep, and gives an excellent exposure of Jurassic beds up to 100 m long. The exposure is composed of uniform gray micaceous quartz-feldspar fine-grained sandstones and is cut by joint cracks of two directions: NE:50°—65° and NW:320°. In addition, a series of disjunctive disturbances is associated with the azimuth NE:50°, accompanied by zones of rock crushing and dipping to the SW at angles of 15° and 45°. Upstream along the river the exposures abruptly break off, and the steep valley slope suddenly passes into an extensive marshy lowland, continuing for about one kilometer and, finally, giving way to the high uplift of Telmin Cape.

The factual material indicated is, of course, insufficient for constructing the second half of our section. It is nevertheless probable that in this sector the compressed folds and thrusts, which occur near the resort park, are less developed; it is also probable that the rather deep subsidence of the Paleozoic, established by exploration within the Yamalaya syncline, is preserved also in the area of the Telmin bog, beyond the sharp break of the Spassky anticline.

The longitudinal section of the left slope of the Angara River considered above, from the village of Nechaeva to the village of Telma, shows that the tectonic structure of the southeastern limb of the Buret-Belsk anticline described in the preceding chapter preserves its features also in the Usolye district: continuing to submerge beneath the level of the Angara River, the Paleozoic limestones form a system of folds of the second order, which, while remaining very gentle on the whole, are in places expressed more sharply, sometimes revealing also thrust phenomena, as is the case in the resort park. We have sufficient grounds to extend the analogy in the principal features of folding still further, to the degree of homology, since the main elements of the folding of the Usolye district, as also farther down the Angara River, are oriented according to a general azimuth NE:50°, or in directions close to it. This is indeed observed at many of the above-mentioned points, and especially at those of them where the sharpest disturbances occur, as well as where the rock outcrops are distinguished by the greatest preservation. The same direction of folding is indicated also by the recorded joint cracks, which are one of the expressions of tangential pressure and are oriented in many cases likewise along azimuths—NE:50°—60°. But in addition to the NE direction of folding, there are undoubtedly others in our district as well, as indicated by direct measurements both of the bedding of the strata, which gave strike azimuths of NW:300°—320° and NE:20°, and of joint cracks, often oriented in the directions—NW:300°—320°, and sometimes NE:10°, 15°, and 25°, and even meridionally. All this points to the considerable complexity of the tectonic structure of the district and raises the question of other directions of folding and of their possible significance for the Usolye deposit.

In the description of the tectonics of the Cheremkhovo district it was indicated that, alongside the northeastern folding, northwestern folding also has substantial importance there.

folding that forms the large Bulai anticline. In order to judge the possible role of this folding in the Usolye district, it is necessary to trace at least one natural section of the Paleozoic in a NE direction, cutting the NW folding. In the immediate vicinity of the town of Usolye there is, unfortunately, no such section; but it is provided by the lower reaches of the B. Belaya River, at a distance of about 10 km from Usolye. In its most general features it may be characterized as follows. The modern valley of the B. Belaya River, subordinating itself to the north-eastern folding, makes in its lower course two sharply expressed bends (Fig. 1), and in the north-eastern direction that interests us it runs only at their crests and in the very lower reaches of the river. At the crest of the first bend, below the village of Malta, the conditions of occurrence of the rocks are very calm: the Paleozoic limestones composing the lowered right slope of the valley, only 5–6 m high, dip very gently to the NE. But at the Klyuchi locality, with the turn of the valley to the NW, they give way to Jurassic rocks, which, in connection with the above-described belt of the Malta dislocations, have a NE strike. No more considerable disturbances of a north-western direction are noticeable here. The crest of the second bend, above the settlement of Badai and the Malta Works, is characterized somewhat differently: throughout the entire length of the north-eastern segment of this bend the Paleozoic limestones crop out on the left slope of the valley, forming heights of up to 8–10 m, and are distinguished by a gentle dip now to the NE, now to the SW, with predominance of the latter direction and with an angle of dip not exceeding 3°–5°; and only at the extreme NE end of the said segment, at the Malta Works, do the limestones form several fairly sharply expressed, though small, north-western folds. The stretch of valley below the settlement of Badai is again characterized by a more or less persistent dip to the NE over a distance of up to 2 km; connected with this is the rapid lowering of the right slope and the probable rather deep sinking of the limestones. But in the very lower reaches of the river the rocks acquire a reverse inclination to the SW; the limestones quickly rise again, forming on the left slope considerable heights reaching up to 20–30 m.

Thus, in the lower reaches of the B. Belaya River two very gentle troughs of NW strike are indicated. These troughs, and especially the first of them, are, it is true, very weakly expressed and might even be attributed to primary irregularities of the sea floor. However, the concordant participation in the gentle dip of considerable limestone strata, as well as the not infrequent small but rather sharply expressed disturbances of the rocks, always concordant with the general gentle dip of the whole sequence, incline us in favor of a tectonic origin for the indicated troughs.

The described stretch of the B. Belaya River, with an azimuth of 320°, characteristic for NW folding, is projected onto the area of the Usolye deposit. But since the nearest points of the stretch lie 6–7 km from the town of Usolye, the tectonic conditions of this stretch may be taken for our deposit only as probable, requiring possible verification on the basis of existing factual material. Such a possibility is provided by exploration boreholes on Spassky Island and the deep borehole of the Barkhatovka mine. Fig. 10 presents a schematic section based on the data from these boreholes¹. It gives a transverse section of the Angara River and outlines a very

a weakly outlined trough of the second order, which then, after a gentle inflection, passes into a fairly deep syncline closer to the Barkhatovskaya pit. The calm character of the Paleozoic subsidence to the NE is confirmed both by the geological conditions of the lower reaches of the Belaya River and by the observational data of recent years in the Irkutsk coal basin, according to which the northeastern limbs of northwestern uplifts are always distinguished by the most gentle and calm forms of occurrence.

The same section, at the same time, shows that the Usolye district is indeed situated on the northeastern limb of the northwestern Bulai anticline mentioned at the beginning of the present article, and also clarifies the origin of those azimuths of northwestern strike and of the jointing cracks of the rocks that are observed in this district. Together with the elements of NE folding, it gives a sufficient explanation for another fact that constituted one of the enigmas of the Usolye deposit—namely: the development on the right slope of the Angara River of a thick sequence of Jurassic deposits, descending near the Barkhatovskaya pit to a depth of up to 100 m, whereas in the Usolye resort Paleozoic limestones, widely distributed also lower down along the left slope, crop out at the surface (Fig. 2). This relation between the right and left slopes of the Angara River attracted the attention of all investigators who in one way or another approached the geology of the Usolye deposit, and in most cases they saw in it the expression of a large fault, which caused the subsidence of the Paleozoic of the right slope to a depth of up to 100 m. At present there is no need to seek here indications of a fault, since the stated relation of the slopes of the Angara River finds its simple explanation in the features of the geological structure of the deposit explained above, being the geometric consequence of the two aforementioned directions of folding and of the relief of the locality. Indeed, the inclusion of the Usolye district within the southeastern limb of the Buret-Belskaya anticline and the northeastern limb of the Bulai anticline, with the meridional direction of the valley of the Angara River below the town of Usolye, makes it entirely understandable that the line of descent of the limestones beneath the level of the Angara River cuts its valley at a very acute angle, as shown in Fig. 2, where this line has been plotted partly on the basis of the author’s personal observations and partly according to scattered data from the local population about outcrops of “limestone.”

As regards, finally, the directions of folding close to the meridional strike, in the Usolye district most often following azimuths of 10°–20°, it should be noted that in the Irkutsk coal basin this folding is encountered rarely. Moreover, it is very probable that the folding of the indicated azimuths belongs to the latest epoch of the Quaternary period and is distinguished by very slight intensity, affecting only the upper horizons of the Jurassic, with rapid attenuation at depth.

On the basis of all that has been said and the data of later investigations in the Irkutsk basin, the possible role of folding of different directions in the genesis of our deposit may be characterized as follows. The latest folding, of a direction close to meridional, may be entirely disregarded in questions of the genesis of the deposit, since it rapidly dies out at depth. The NW-trending folding is very ancient, and its first manifestations in the Irkutsk basin may date back to the very beginning of the Paleozoic. To it belong broad and gentle folds extending for more than 100 km, and, by this fact alone, probably embracing the entire thickness of the Irkutsk Paleozoic. Hence it is clear that, even with the gentle dip of the Paleozoic, in which it chiefly finds its expression in the Usolye district, it may have played an essential role in the bedded circulation of brines. But all the peculiarities of the regime of the springs, wells,

and of the boreholes of the Usolskoye deposit, as well as of the underground circulation of waters, must most of all be connected with the NE folding, which manifested itself here most sharply and left the greatest imprint on the orography of the locality and the texture of the underlying rocks. Taking into account this role of the NE folding, we shall dwell on it in greater detail.

The factual material of more recent investigations gives grounds for asserting that folding of the NE direction in the Irkutsk coal-bearing basin manifested itself several times: one of the phases of this folding ended on the eve of the lacustrine epoch of the Middle Jurassic, and the last was considerably later, probably already in the Cretaceous period, when it also affected the Jurassic deposits. The first phase of folding¹ evidently took place shortly before the formation of the Irkutsk Jurassic lakes, since even with the generally weak manifestation of it, denudation did not have time to destroy the gently undulating relief forms created by it, and it exerted a great influence on the facies distribution of the coal-bearing Jurassic sediments. However, even in that short interval of time which passed before the deposition of these rocks, denudation accumulated a noticeable amount of eluvial and deluvial material, then carried it down into synclinal depressions or new depressions, which it easily created along sectors of tectonically crumpled rocks. Hence, the profile of the Paleozoic, shown in the sections of figs. 5, 6, and 7, must be understood only as the Middle Jurassic surface relief and at the same time the relief of the bottom of the Jurassic lake, in which are expressed, on the one hand, the softened forms of NE folding (fig. 9), and, on the other, secondary depressions along zones of strong crumpling, prepared by denudation—such as, for example, should to a considerable degree be credited with the formation of the deep and narrow depression of the Almaznaya syncline².

After this the NE folding recurred long after the lacustrine epoch of the Jurassic, probably already in the Cretaceous period, when the coal-bearing deposits had diagenetically already become more or less consolidated. To this new phase are due, most likely chiefly, the disjunctive manifestations of folding and the associated crumpled zones of rocks both in the Jurassic and in the underlying Paleozoic formations. The latter circumstance makes the Cretaceous phase of NE folding especially important for the Usolskoye deposit, since with it must be connected those tectonic fractures and crumpling zones which serve as conduits for brines.

Thus, the factual material of field observations in the vicinity of the deposit has made it possible for us to present a scheme of the tectonic structure of the district, which, however, has a very approximate significance in view of the considerations set forth above. But, using the materials of deep drilling, as well as the data of the small-scale exploration of 1925, we can to some extent refine this scheme, especially in its most critical part—near Varnichny Island and the resort park.

In accordance with the role, clarified above, of the various directions of folding, the chief task of the exploratory work of 1925 was set as follows: to obtain data for constructing an accurate section along the left slope of the Angara River in that part of it which is connected by northeastern folding with Varnichny Island; and also to tie this section to the section of the island on the basis of

data from drilling in previous years, and, in this way, the determination of the position of each well and each deep borehole in the tectonic scheme obtained¹.

The data from these works, as well as the materials of the old explorations, served as the basis for constructing a number of the sections described below.

The section in Fig. 11 is constructed from the point where the pontoon crosses the left bank of the Angara River and farther downstream, along the curved line of the bank to the first natural outcrop of the Paleozoic at Izvestkovy Cape. Above the section, all the deep boreholes of Varnichny Island are shown by black circles. They are projected onto the left side of the Angara River along the azimuth line NE: 47°, which is adopted for this small part of the district as the mean of the azimuth 50° observed in the outcrops of the resort park, and the azimuth of the line of natural outlets of the brine springs, which, according to many years’ observations by mining engineer A. I. Sosov, (46; 14) runs in the direction NE: 45°². From the section it is evident what position the deep boreholes occupy in the folds that have been outlined. In Fig. 12 a section of Varnichny Island is also constructed along the line of boreholes: No. 1, No. 3, and Brodovich’s borehole. Borehole No. 2, located aside from the section line, is projected onto it along the adopted azimuth NE: 47°. The distorted scale adopted in the sections, with a ratio of length to height equal to 1/10, gives an incorrect impression of the southern part of the sections, where the most compressed folds occur. Therefore in Fig. 11-a a third section of the small resort area is placed, with the normal ratio of the scales of lengths and heights, equal to the scale of lengths in the first two sections.

The complete correspondence of the sections of Varnichny Island and of the left slope of the river leaves no doubt. The greater distances between the boreholes in the section of Varnichny Island are explained by the fact that the direction of section adopted here cuts the azimuth NE: 47°, along which these boreholes are projected onto the section of the left slope, at a very acute angle—wherefore the folds of this section appear somewhat stretched. As regards the deeper occurrence, in the corresponding folds, of the upper boundary of the Paleozoic limestones shown on the section of Varnichny Island, it finds its explanation in the general northeastward sinking of the Paleozoic already clarified above.

A certain addition, and at the same time a check on the sections constructed, is provided by another section along the northeastern margin of Varnichny Island, along the line:

borehole No. 5, 1915; brine well No. 3; borehole No. 2, 1925; and borehole No. 1. This section, constructed in Fig. 13, outlines in rough form the same tectonic elements.

Finally, Fig. 14 gives a schematic sketch of a crumpled fold of limestones in the park of the resort, with a clearly expressed upthrow in the hinge and a weak crumpling on the southeastern limb. The crumpled belt of this fold is distinguished by strong silicification of the limestones, by the development of siliceous—mostly irregular—veinlets and lenses, and also by a great development of clay, often ground up, which in places converts the limestone into calcareous rubble. On the northwestern limb, attention is also drawn to the uneven magnitude of the dip of the limestones, which at the upthrow fissure reaches 50°, while with distance from it it decreases to 9°. The strike of this upthrow is NE: 50°.

The series of newly presented sections of the deposit, for the reasons explained above, also gives only an approximate idea of the folded character of the Usolye formations, which in reality must be somewhat more sharply expressed. And after analyzing the stratigraphic composition of the deposit we shall see that there may be other interpretations both of the scale and of the forms of the folding (Fig. 17)¹. Nevertheless, all these sections generally confirm the scheme of folding that was outlined in Fig. 9 on the basis of field observations alone. But neither these sections nor the previously presented material on the tectonics of the Cheremkhovo district resolve the question of the magnitude of the vertical displacements of the rock beds in connection with the disturbances, and, still less, of the depth to which these disturbances penetrate into the Paleozoic sequence—something that is of great importance for understanding the deposit. In view of this, an attempt is made below to resolve these questions, insofar as possible, on the basis of the factual material at our disposal.

The principal question here is the connection between tectonic disturbances observed near the ground surface and the deep horizons where the salt-bearing strata occur, or, in other words, the pathways that serve as conduits for saline brines from great depth. This connection, naturally, must first of all be made dependent on the scale and intensity of the recorded disturbances. From this point of view, the factual material presented above gives rather a negative answer to the question posed, since the very slight intensity of all the recorded disturbances may cast doubt on their having any significance for ascending currents of brines. However, in the study of ore deposits another method is often applied for deciding the question of the continuation to depth of tectonic fissures and the ore veins associated with them. It is usually assumed that veins traced for a more or less considerable distance along strike also have a considerable development in depth; short veins, however, are quickly lost with depth (24: 7). By this criterion, the disturbances of the Usolye deposit must have considerable development at depth, since some of them are traceable for a great distance along strike. This was also noted in the geological description of the Cheremkhovo district, where many belts of disturbance are traced for a distance of more than 10 km, as shown on the map in Fig. 1; and the principal elements of the folding of the southeastern limb of the Buret-Belskaya anticline, which plunges to the southeast, persist throughout the entire watershed area of the Angara and Belaya rivers. This applies fully also to the area of the Usolye deposit, which forms part of the same southeastern limb of the Buret-Belskaya anticline and here, too, preserves all the features of its tectonic structure. Of the individual disturbances of the deposit, the best traced along strike is the main belt of disturbances, running from the resort park through the upper half of Varnichny Island and passing over to Spassky Island and even

¹ See p. 37.

on the right bank of the Angara River. Associated with it is a series of long-recorded natural outlets of saline springs, known in the resort park, on Varnichny and Spassky Islands, and also brines on the right bank of the river near the village of Barkhatova. In addition, according to mining engineer A. I. Sosov, a line of saline-spring outlets, oriented at an azimuth of 45°, can be traced along strike from the resort park for a distance of more than 1 km. Thus, at least the most important disturbances of the Usolye deposit have a fairly considerable development along strike, and therefore one must expect their considerable development also at depth.

This conclusion is fully consistent with the data of deep drilling, which also make it possible to draw certain conclusions about the tectonic structure of the Paleozoic limestones at great depth. In this respect, the materials of the Diamond borehole deserve the greatest attention; it is the only one of all the deep boreholes of Usolye that yielded samples of the rocks penetrated in the form of drill cores, which constitute entirely reliable material. In the section of this borehole, examined in detail in the chapter on stratigraphy, we find the following indications.

1. At the 55 m horizon the borehole passes through resinous and, below, siliceous limestone with vertical veinlets of calcite, total thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 m.

2. The 77 m horizon is marked by signs of brine: “the core is saturated with salt”¹.

3. At 79.60 m. Destroyed limestone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.66 m.

4. » 90.87 m. Siliceous limestone with pyrite in vertical fractures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.47 m.

5. At 99.02 m. Siliceous limestone with vertical fractures and “worms” of silica . . . . . . . . . . . . . . . . . . . . 1.17 m.

6. At 102.67 m. The same . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.51 m.

7. » 106.95 m. Siliceous limestone with vertical fractures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.12 m.

8. » 112.43 m. Vesicular limestone with a vertical veinlet of calcite and salt . . . . . . . . . . . . . . . . . . . . . 1.12 m.

9. At 113.65 m. Vesicular limestone passing into calcareous rubble, cemented by white clay . . . . . . . . 2.85 m.

10. At 118.22 m. Dolomitized limestone passing into rubble.

11. From 120.66 m to 121.27 m. “The core is saturated with salt.”

12. At 125.56 m. Dolomitized limestone passing into rubble and then into clayey shale . . . . . . . . . . 0.71 m.

13. At 127.39 m. Calcareous rubble, cemented by white clay, passing below into clayey shale; then follows destroyed limestone, passing into limestone, vertically cracked; below again comes destroyed limestone, passing into shale; farther on, dolomitized destroyed limestone interbedded with shale. Total thickness of this horizon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.23 m.

14. At 254.46 m. Shaly, readily disintegrating limestone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.91 m.

15. » 284 m. Destroyed limestone, cemented by shale, readily crumbling . . . . . . . . . . . . . . . . . . . . . . . 1.83 m.

These selections from the section of the Diamond borehole show that at various horizons of the Cambrian limestone sequence, and especially at a depth of 100–130 m, there are clear traces of tectonic disturbances, and that these disturbances

bear all the features described above of strongly disturbed rocks, which accompany the phenomenon of thrusts and the crumpled folds often connected with them. They also indicate the large number of such disturbances and the fact that it is precisely with them that the circulation of saline brines is connected, which in the Almaznaya borehole was established at three horizons: 77.46; 112.43; 120.66 m.

Unfortunately, the other deep boreholes, drilled with the Keystone drill and yielding only so-called drill sludge, give us less clear indications. Nevertheless, even in them we sometimes find signs of tectonic disturbances. For example, in Brodovich’s borehole, at the 65-meter horizon, calcareous rubble with inclusions of gypsum, about 32 meters thick, was encountered, which indicates a major disturbance intersected by the borehole. The same is probably indicated also by the fine interbedding of limestones, clays, and argillaceous shales recorded in borehole No. 2 at a depth of 250–300 m.

The cited references from the data of deep drilling confirm the conclusion drawn above concerning the considerable development at depth of tectonic disturbances in the Usolye district. They do not, it is true, solve the question of the forms and character of their connection with surface disturbances, but they may serve as a sufficiently precise framework for the geometrical expression of such a connection.

On the basis of the totality of all the data relating to our deposit, an attempt has been made in Fig. 15 to give a graphic representation of the most probable tectonic structure of the Paleozoic sequence of Usolye, and at the same time to connect the disturbances at different horizons. The construction of the scheme in Fig. 15 is based on the following facts and considerations.

1. The Paleozoic limestones of the district, lying almost horizontally, are characterized by numerous gentle folds, with which small thrusts and zones of crushed rocks are often associated.

2. The planes of the overthrusts are always rather steeply inclined; but their angle of dip in many cases rapidly decreases down the dip, in connection with which the thrust often passes into a bedding-plane displacement and dies out altogether.

3. The thrust portions of the folds lie more or less quietly; but in the root parts of the disturbance, zones of very intense pressure are often observed, with typical tectonites at the plane of displacement and other tectonoclasts on its lower side.

4. The tectonic disturbances of the deposit are due chiefly to tangential pressure coming from the NW¹; they probably occurred at the beginning of the Middle Jurassic epoch and then were repeated after the Jurassic, i.e., at a time when the Paleozoic limestones, now assigned to the Cambrian system, had already lost all their plastic properties and for the most part had passed into crystalline varieties of limestone.

5. The tangential pressure, which served as the normal expression of the phenomenon of contraction (25; 17–18) on the segment of the lithosphere of the extensive Irkutsk amphitheater, acted both on the underlying slab of crystalline Precambrian rocks and on the sequence of Cambrian rocks covering it, which by that time were already quite firmly cemented diagenetically. In producing tectonic movements in the slab, probably of the type of deep-seated overthrusts (26; 150), this pressure strove to displace from it the Cambrian sequence, in which it created rather complex tectonic interrelations.

6. The mechanical stresses within the Cambrian sequence, initially oriented horizontally, under conditions of varying rock composition, their insignificant thickness, and hence their proximity to the surface, were decomposed, being resolved along numerous secondary surfaces of a scalloped character

at depth and by more or less steeply set planes nearer to the surface, forming, as a result, a system of disturbances in the form, as it were, of branching zones of crumpling and overthrusts, as is shown schematically in Fig. 16.

1. Hence, the principal type of disturbances of the Usolskoye deposit, as composed of a very gently dipping Paleozoic formation (27; 57), is longitudinal displacements. Subordinate to them are zones of crumpling that branch off from them in a fan-like manner, numerous and often small overthrusts, and minor differential movements. We have here, therefore, those disturbances which, according to modern views, are most normal for ancient and rigid geological formations (27; 22; 28, 168).

The tectonic scheme of the deposit outlined above makes clear the connection of surface disturbances with the deep horizons of the Paleozoic, and simply resolves the question of those pathways that serve as conduits for brines to the daytime surface. With such a solution of the main question for the deposit, another question—concerning the magnitude of vertical displacements of the rocks—loses its acuteness. For each individual case this magnitude is very small, but the sum of all displacements of a single zone of crumpling may attain a rather large value, an approximate idea of which can be given to us only by the stratigraphic correlations made in the following chapter.

The tectonic structure of the deposit, characterized above, is shown in plan in Fig. 4, where the zones of greatest enrichment by brines are also shown, fully consistent with our tectonic scheme.¹)

STRATIGRAPHY.

Composition of the Usolskoye deposit.

In the region of the town of Usolye three geological formations are developed: recent deposits of the Angara River and its tributaries, the Jurassic coal-bearing suite, and a thickness of saline Paleozoic rocks belonging to the Middle Cambrian.

Recent deposits are connected exclusively with the valley of the Angara River and its small tributaries—the streams Telmy, Skipidarka, and Shelestekha—and are represented by clays, sands, and pebbles, more often forming mixed sandy-clayey and sandy-pebbly accumulations. They have an insignificant thickness: according to the data of the old explorations, up to 13 m; according to the data of the 1925 exploration, up to 7 m. They attain their greatest thickness in the marginal parts of the valley, where they often compose the modern meadow terrace, and also along the shores of the islands. The numerous islands of the Angara River, in their marginal sections, most often are wholly composed of these deposits, developed also considerably below the modern river level; but in the central parts of the islands they are distinguished by small thickness or are even entirely absent. Hence, among other things, it follows that a large part—at least—of the large Angara islands is primary, and only along their margins are they often greatly enlarged at the expense of the river’s loose deposits. It should be noted here that this conclusion fully coincides with the data of the old exploration only where there are no Jurassic rocks beneath the river deposits, and where the thickness of the recent sands and pebbles does not exceed one or two meters (sta—

¹) In the above outline of the tectonic structure of the deposit, an important question has not been touched upon: the temporal interrelation of the principal directions of folding, since the area of the deposit does not provide the factual material necessary for resolving it. Let us note, nevertheless, that folding of the direction close to meridional (NE: 10°—20°), apparently the youngest in age, belongs to Quaternary time; whereas the folding of the two other directions (NE: 50°—60° and NW: 320°) manifested itself many times, and its first phases must be assigned to the Paleozoic. The question of their age interrelation requires special analysis.

wells and borehole No. 2 on Varnichnyi Island, Fig. 3). But where the presence of the Carboniferous is to be presumed, the thickness of the Angara deposits, according to the old exploration and in the central parts of the islands, is rather considerable: for example, on Spasskii Island these deposits reach 8–9 m according to the drilling logs of 1915, and on Varnichnyi Island even up to 13 m (borehole No. 1). Such sharp divergence from the data of the 1925 exploration is easily explained: the Jurassic deposits in their upper horizons, as we shall see somewhat below, are always in a weathered state, and it is understandable that samples from the drilling tools that passed through them yielded loose clay or loose sand not only from the horizons of modern deposits, but also from the Jurassic horizons. An error is especially possible here in those cases where normal Jurassic deposits are overlain by the eluvium of the Jurassic, which usually appears in the form of sandy-pebbly accumulations and requires special investigations to distinguish it from river formations.

The three named types of river deposits—clays, sands, and pebbles—usually follow in a definite order, namely: above, both on the valley’s bank terraces and on the islands, there almost always lies clayey sand, passing downward sometimes into clean sand; still lower comes sandy pebble, after which already follow Jurassic deposits or Paleozoic. In some cases an alternation of deposits is observed; for example: beneath the upper clays and sands with pebbles there again come clayey sands, passing into pebble. In Appendix IV a whole series of sections of boreholes from the 1925 exploration is given, providing an idea of the composition and thickness of the river deposits. A typical one among them may be considered the section in borehole No. 2, which gives the following beds in descending order:

1. Clayey sand . . . . . . thickness 2.1 m.
2. The same with pebble . . . . . » 0.6 »
3. Sand with pebble . . . . . . » 2.2 »
4. Sand . . . . . . . . . . » 0.7 »
5. Sand with pebble . . . . . . » 0.9 »
6. Jurassic eluvium . . . . . . » —

With very small thickness and limited horizontal distribution, the modern deposits cannot have great significance in the geology of our deposit.¹

The Carboniferous in the Usol’e district is distinguished by uneven development. It forms a thick mass on the right side of the Angara River, making up here bank elevations more than 70 m high, and descending below the river level to a depth of up to 100 m. On the left side these deposits attain considerable thickness only above Varnichnyi Island, where they descend below the water level to a depth of at least 40 m, and above the match factory and the mouth of the Skitidarka River they form bank elevations up to 15 m high. But from the park of the Usol’e resort and Varnichnyi Island downstream along the Angara River, where Paleozoic limestones crop out in many places, the Jurassic deposits have only very limited distribution, filling only synclinal depressions and having a thickness of only 2–6 meters.

Within the Jurassic, as adopted on the geological map (Fig. 2) for the Usol’e district, two types of these deposits must be distinguished. One, named by us the Olonki type (33; 25) after its characteristic manifestation in the environs of the village of Olonki, is developed on the northern margin of the district, along the right bank of the Angara River from Soroch’ya Pad, above the mouth of the Uliakha River, and along the left bank approximately from the village of Zaitseva. In the remaining part of the district, along both banks

another, the Barkhatov type of Jurassic deposits, is developed on the Angara River¹. The first of these is characterized by the substantial participation in its composition of loose sandy conglomerates and light yellowish-gray, medium- and coarse-grained quartz–feldspar sandstones, which upon weathering form characteristic accumulations in the bank bluffs of a light-colored sandy–pebble mass. At the indicated points (the village of Sorochya) these deposits are overlain by the Barkhatov Jurassic, in which, judging by the outcrops above the level of the Angara River, pebbles play an already scarcely noticeable role, being preserved only in the form of rare stringers; instead, firm gray, fine- and medium-grained, calcareous, micaceous–feldspathic sandstones are developed². In the composition of both types of Jurassic, argillites also take part; they usually form distinct horizons and contain beds of coal and carbonaceous shales.

The nearest small outcrop of the Olonki formation to the town of Usolye is observed on the left bank of the Angara River, opposite Zaitsev Island, and a more considerable one in thickness occurs lower down, near Nechaeva Island. But fuller and more characteristic outcrops of this formation are developed immediately below the settlement of Badai, on the right bank of the B. Belaya River, and in the area of the village of Olonki along the right slope of the Angara River, as well as above the mouth of the Ulyakha River, where they form, by the very road, a rather high cape, with a thickness of white, almost loose sands, interbedded with pebbles, well exposed thanks to road clearing.

As for the Barkhatov Jurassic, a sufficient idea of it is provided by the good exposures near the match factory and higher up the valley, especially by the large exposure before the Telma bog, composed for its entire height, up to 12–15 m, of uniform gray micaceous–feldspathic, rather firm sandstones. Jurassic sandstones of the same character also occur at the resort park, where they form a small terrace at the descent to the pontoon.

The same Jurassic deposits were penetrated by deep borehole No. 1 on Varnichny Island and by all the exploratory boreholes on Spassky Island; their sections, given in Appendices I and II, provide sufficient material for establishing the following composition of the very lowest part of the Barkhatov Jurassic. Here the sandstones always pass into clays, which are interbedded with coal seams and constitute a persistent horizon, decidedly in all the boreholes, of rather considerable thickness, varying from 6 to 10 and even 12 m (borehole No. 5, 1899, and borehole No. 4, 1915). Still lower there again follow sands and sandstones, interbedded with small layers of clay and having a thickness of 2–4 m (boreholes No. 3 and No. 4, 1915). The entire Jurassic sequence is underlain, finally, by clays with angular fragments of flint and siliceous limestone, which already lie upon the Paleozoic. The aforementioned carbonaceous–clayey horizon deserves special attention, being distinguished by considerable thickness. The question of its coal content, however, has not yet been sufficiently clarified, since the industrial thickness of the coal has been established on Spassky Island only in borehole No. 2 of the 1899 exploration, which encountered a coal seam 1.67 m thick. In oth—

in the same boreholes there is mention only of pieces of coal encountered among other rocks, or, more often, of “carbonaceous” earth. Nevertheless, qualitatively, its coal-bearing character has been established at many points. Thus, on the left bank of the Angara River, a cape above the pontoon deserves mention, where a small coal seam was identified as early as 1895 by mining engineer A. I. Sosov. At a distance of about 100 meters from there is the Diamond borehole in the park of the resort, which also encountered coal; and 200 m away, in the yard of the factory office, borehole No. 1, drilled in 1899, encountered at a depth of about 3 m three coal seams with a total thickness of more than 1 m. In the same respect, attention is deserved by the cape of the match factory, in which coal 16 cm thick is exposed. All this indicates that the coal-bearing character of the lower Jurassic horizons near the town of Usolye has now been fully proved. As for the presence in them of coal seams of industrial thickness, this question can be resolved only by carrying out proper prospecting by means of drilling and shafting, since the exploration for coal hitherto conducted in the Usolye district, apart from the above-mentioned boreholes on Spasskii Island, did not include these horizons.

To the characterization of the Jurassic one must also add that in our district, as throughout the Irkutsk basin, these deposits weather rapidly, and in horizons that come to the surface or lie close to it they often turn into a sandy-clayey or sandy-pebbly mass which, as a result of subsequent washing by atmospheric waters on watershed heights and on the bank slopes of river valleys, often gives accumulations of clean sands and pebbles. Such loose eluvial-deluvial remnants of the Jurassic are difficult to distinguish from later formations, and were the reason why, on geological maps of the basin, Tertiary lacustrine and post-Pliocene river deposits were placed where undoubtedly Jurassic strata are present (10; pl. 1, 2). The same type of eluvial remnants of the Jurassic in the form of sands and pebbles was the reason for an erroneous determination of the thickness of modern deposits of the Angara River in boreholes of the Usolye district as well.

In concluding the description of the Jurassic deposits, it is necessary to touch upon one more rock, which always occupies an intermediate position between the Jurassic and the Paleozoic and which is very unevenly developed in the district. This rock is called a siliceous breccia by K. I. Bogdanovich (10;151,252), and M. K. Korovin (19;39) called it a breccia-like conglomerate. On the basis of later investigations in the basin, it must be noted that here two types of this rock must be distinguished: in one, large and small, angular and weakly rounded fragments of flint and siliceous limestone are cemented by marly limestone; in the other, the same fragments are cemented by clay or argillite. The first type should be called a breccia-like limestone conglomerate or breccia-like limestone; it is undoubtedly of Paleozoic age and occurs, for example, near the village of Olonki, but has not been found near the town of Usolye itself. The second, usually overlying the first, should be called a clayey breccia-like conglomerate.¹ It may have various origins. In one case the clayey cement is the residual product of leaching by groundwater of the marly limestone cement of the first rock—which must have taken place after its formation and could have ended in pre-Jurassic time. In another case, the siliceous fragments, as an eluvial-deluvial remnant of the Paleozoic, could have acquired a clayey cement together with the accumulation of fragmental material before the beginning of the lacustrine epoch of the Jurassic, or, finally, at the bottom of an already Jurassic lake. Only in this last case should the breccia-like clayey conglomerate be included in the coal-bearing Jurassic formation. But how simple it is to distinguish the Paleozoic limestone breccia-like conglomerate from

of the clayey type, that it is so difficult to draw a boundary between the indicated varieties of the latter. This can be done only by direct study, on the spot, of the conditions under which the rock occurs.

The clayey breccia-like conglomerate is considerably developed at Usolye, but rarely reaches a thickness of more than 10 m, which occurs only in compressed synclinal depressions, as, for example, in the Almaznaya syncline. In the crest parts of anticlines it is either entirely absent or has insignificant thickness. In drilling, this rock constitutes one of the very characteristic horizons, since it indicates the proximity of the Paleozoic limestones, and at the same time is very easily recognized.

Paleozoic deposits have the most important significance in the geology of the Usolye deposit. But, unfortunately, it is precisely for this formation that we at present possess incomplete data, since in the area of the deposit only the upper horizons of it, rarely more than 10–15 m thick, come to the surface; the data from deep drilling, carried out under the unfavorable conditions described at the beginning of this article, do not always give a clear idea of the composition of the rocks. Therefore, as a supplement to the materials from the deep boreholes, it is useful first to become acquainted with the composition of the Paleozoic in the nearest parts of the Irkutsk coal basin, for example along the B. Belaya River, in the Bel’sk-Kholmushino area, where the thickness of the limestones exposed at the surface reaches 160 m, and where, according to all data, we have the same horizons of the Irkutsk Paleozoic. The section of this series in the named area, according to M. K. Korovin, has the following composition in descending order (20; 708):

1. Marly limestones, light-gray and banded, often interbedded with greenish, bluish, sometimes dark hornstones and cherts, always thin-platy . . . . . . . . . . . . 10 m.

2. Light-gray and ash-gray marly limestones, sometimes pure varieties of limestones, more or less dolomitized, more rarely concretionary, more often thin-platy, sometimes medium-platy . . . . . . . . . . . . 30 m.

3. Dolomitized, sometimes concretionary limestones, dense or fine-grained, light- and yellowish-gray, more rarely greenish-gray, in the lower half alternating with gray and dark-gray, usually medium-platy . . . . . . . . . . . . 50 m.

4. Dark-gray, always distinctly granular, bituminous concretionary limestones, often coarsely cavernous, sometimes breccia-like, always massive, with coarse prismatic jointing . . . . . . . . . . . . 70 m.

Total . . . . . 160 m.

Above the described limestone series along the B. Belaya River, in places, there is observed the development of calcareous breccia-like conglomerates no more than 2–4 m thick, passing upward in many cases into a clayey breccia-like conglomerate with refractory clays, already overlain by coal-bearing Jurassic deposits.

In the Usolye area the limestone series of the Paleozoic evidently begins with the same horizons of the Belaya River, since, in addition to the described clayey breccia-like conglomerate, which crops out in several places and has been recorded by many boreholes as “clay with siliceous breccia,” or simply “clay with flint,” in many localities, such as Izvestkovyi Mys or the Zaitsev anticline, there is observed above a thin-platy marly light-gray limestone, passing downward into a gray, more coarsely platy one¹. As for the lower horizons of the Paleozoic, the only

material concerning them is provided to us by deep drilling, which, unfortunately, is of relative value for stratigraphy, since all the deep boreholes, except one, were drilled with a Keystone bit. Under these conditions, understandably, we are deprived of the possibility of giving a more detailed stratigraphic subdivision of the Paleozoic, and therefore below we confine ourselves to an attempt to give only a scheme of the stratigraphy, distinguishing in a series about 770 m thick only three stages. Such a subdivision may receive factual justification, since down to a depth of 160 m we have the above-mentioned data from the study of direct outcrops of the Paleozoic; down to a depth of 360 m—the data of the Diamond borehole, which constitute entirely reliable material; while from a depth of 690 m begins the salt-bearing stage, whose individuality is beyond doubt. Least well characterized is the limestone sequence covering the salt-bearing deposits and developed from a depth of 360 m to 690 m, since it is represented only by drill cuttings from Keystone-bit samples. But this part of the section, according to the concordant data of all the boreholes, is lithologically very homogeneous, and its stratigraphic position also can hardly arouse serious doubts.

For judging the composition of the individual stages, Appendix III gives, with certain generalizations of the beds, the sections of all the deep boreholes of Usolye. The section of the Diamond borehole, in view of its important significance, is given below in full as well¹).

No. in order	Name of rock	Depth from surface (m)	Bed thickness (m)
1	Coarse sand with pebbles	—	0.96
2	Yellowish-gray plastic clay with interbeds of decomposed brown coal	0.96	1.25
3	Grayish plastic clay	2.21	0.83
4	Whitish-yellow clay	3.04	1.40
5	Brown coal with thin interbeds of clay	4.44	0.89
6	Whitish-yellow clay	5.33	1.27
7	Gray clay, very hard, refractory (so-called crystalline), with small inclusions (concretions) of silica	6.60	9.02
8	Siliceous concretions of grayish color, cemented by crystalline clay, very hard, although they have a layered structure. The clay, moreover, is gray, very hard, refractory	15.62	2.06
9	Siliceous limestone of brown color with a coating of crystalline calcareous spar and inclusion of sulfur pyrite. On being struck, the limestone gave off a resinous odor	17.68	0.05
10	Siliceous concretions of grayish color, cemented by brown clay. The concretions contain inclusions of sulfur pyrite, sometimes with coatings of calcareous spar.	17.73	15.63

¹) The section given below represents an excerpt from the drilling log, preserving the nomenclature of the original. The depth and thickness of the rock beds, given in feet, have been converted into meters.

No. in order	Name of rock	Deepened from the surface, meters	Thickness of bed, meters
11	Siliceous dolomitized limestone, gray in color, very hard; reacts poorly with acids; with rare inclusions of iron pyrite.	33.36	10.48
12	Siliceous limestone	43.84	0.66
13	Siliceous limestone with an inclusion of iron pyrite and interbeds of flint (hornstone)	44.50	2.81
14	Resinous limestone with vertical interbeds of spar	47.31	0.13
15	Siliceous limestone with vertical interbeds of calcareous spar, with inclusions of pyrite	47.44	4.47
16	Siliceous limestone	51.91	2.72
17	Dolomitized limestone	54.63	0.71
18	Siliceous limestone; saturated with iron pyrite	55.34	2.08
19	Siliceous limestone	57.42	0.38
20	Limestone saturated with pyrite	57.80	0.79
21	Brown limestone saturated with pyrite	58.59	6.13
22	Dolomitized limestone, very dense	64.72	1.47
23	The same, less dense	66.19	1.62
24	Dolomitized limestone, thin-bedded	67.81	2.01
25	Dolomitized limestone saturated with iron pyrite, with interbeds of black flint	69.82	2.06
26	Siliceous limestone, interbedded with variously colored flints; saturated with pyrite, very hard	71.88	0.89
27	Siliceous limestone	72.77	0.94
28	The same, cavernous, with dense flint	73.71	3.81
29	Dolomitized limestone with interbeds of iron pyrite and hornstone. Signs of brine; the core is saturated with salt	77.52	1.19
30	Siliceous limestone, abundantly saturated with pyrite	78.71	0.81
31	Dolomitized limestone with interbeds of hornstone and iron pyrite	79.52	0.43
32	Broken limestone	79.95	0.66
33	Siliceous limestone with interbeds of pyrite	80.61	2.64
34	Siliceous limestone	83.25	3.20
35	Siliceous limestone; finely saturated and interbedded with pyrite	86.45	1.17

No. in order	Name of rock	Depth from surface, m	Bed thickness, m
36	Siliceous limestone	87,62	3,28
37	Siliceous limestone, saturated with pyrite in vertical fissures	90,90	2,47
38	Siliceous limestone	93,37	1,27
39	Siliceous limestone with an inclusion of pyrite	94,64	0,91
40	Siliceous limestone	95,55	3,63
41	Siliceous limestone with vertical fissures and “worms” of silica	99,18	1,16
42	Siliceous limestone, hard, saturated with pyrite	100,34	0,69
43	Siliceous limestone with interbeds of hornstone and pyrite	101,03	1,72
44	Siliceous, very hard limestone with “worms” of silica and interbeds of pyrite	102,75	0,50
45	The same, with interbeds of 2″ of pyrite	103,25	1,57
46	Siliceous limestone, dense	104,82	2,11
47	Siliceous limestone with vertical fissures filled with spar	106,93	1,12
48	Siliceous limestone, very hard	108,05	4,32
49	Siliceous limestone with interbeds of cherty hornstone	112,37	0,15
50	Cavernous limestone with a vertical fissure, partly overgrown with spar; contains salt	112,52	1,12
51	Siliceous limestone passing into cavernous rubble. The limestone rubble is cemented with white clay	113,64	1,22
52	Siliceous limestone	114,86	1,50
53	Limestone with interbeds of silica	116,36	1,12
54	Dolomitized limestone	117,48	0,79
55	Dolomitized limestone, passing in places into rubble. The borehole is saturated with salt	118,27	2,74
56	Dolomitized limestone	121,01	4,50
57	Dolomitized limestone, passing in places into rubble and, at the end, into clay shale	125,51	0,71
58	Clay shale	126,22	0,46
59	Limestone	126,68	0,61
60	Calcareous nodules cemented by white clay	127,29	0,15

Nos. in order	Name of rock	Depth from surface, m	Bed thickness, m
61	Argillaceous shale	127.44	0.15
62	Soft, disintegrated limestone	127.59	0.91
63	Limestone, vertically jointed	128.50	0.61
64	Disintegrated limestone	129.11	0.91
65	Vertically jointed limestone	130.02	0.25
66	Disintegrated limestone, passing into shale	130.27	1.47
67	Dolomitized limestone, partly disintegrated; in places passes into shale	131.74	3.96
68	Dolomitized limestone	135.70	17.40
69	Dolomitized limestone, in places passing into shale	153.10	8.01
70	Dolomitized limestone, dense, hard	161.11	5.28
71	The same, less dense	166.39	4.45
72	Dolomitized limestone with inclusions of siliceous interbeds	170.84	6.35
73	Siliceous whitish limestone	177.19	20.25
74	Siliceous limestone, dark brown	197.44	3.71
75	Siliceous, very hard brown limestone	201.15	7.55
76	The same, irregularly bedded	208.70	6.13
77	Siliceous limestone	214.83	8.87
78	Siliceous fractured limestone	223.70	6.65
79	Siliceous limestone	230.35	6.33
80	Siliceous limestone, in places very hard	236.68	3.84
81	Argillaceous shale	240.52	0.35
82	Siliceous limestone, in places very hard. The columns are strongly saturated with salt	240.87	12.68
83	Dolomitized limestone, in places shaly	253.55	1.48
84	Shaly limestone, in places easily disintegrating	255.03	0.91
85	Dolomitized limestone with small interbeds of shale	255.94	4.11
86	Siliceous limestone; in places passes into nodule-bearing, finely crumbling limestone	260.05	21.03
87	Interbed of shale	281.08	0.13

No. in order	Name of rock	Depth from the surface, m	Thickness of bed, m
88	Siliceous limestone	281,21	4.30
89	Disintegrated limestone, cemented with shale; crumbles easily	285,51	1,83
90	Clayey dark shale, soft	287,34	0,61
91	Limestone	287,95	10,75
92	Siliceous interbed, very hard	298,70	0,25
93	Limestone	298,95	5,61
94	Anhydrite (gypsum)	304,56	0,91
95	Limestone with interbeds of anhydrite	305,47	2,44
96	Limestone with frequent but thin interbeds of gypsum	307,91	1,35
97	Shale with interbeds of gypsum	309,26	0,26
98	Limestone	309,52	6,33
99	Interbeds of gypsum (dolomite)	315,85	0,96
100	Limestone. Column with salt incrustation	316,81	13,15
101	Interbed of anhydrite	329,96	0,15
102	Limestone	330,11	4,91
103	Interbeds of siliceous hornstone	335,02	0,10
104	Limestone	335,12	1,22
105	Limestone with interbeds of gypsum	336,34	0,48
106	Limestone	336,82	1,67
107	Same, with small interbeds of gypsum	338,49	0,33
108	Limestone	338,82	0,41
109	Marly limestone, with interbeds of gypsum	339,23	0.35
110	Rock crumbles, although by its properties it is a very dense dolomitized limestone	339,58	0,25
111	Limestone	339,83	6,65
112	Quartzite; alternating with flints	346,48	0,25
113	Limestone	346,73	15,95
114	Flint	362,68	0,10
115	Limestone	362,78	—
	TOTAL	362,78	—

In the section presented for the Almaznaya borehole, down to a depth of 6.5 m there are Jurassic deposits; below, to a depth of 34 m, a fairly thick horizon of breccia-like conglomerate with refractory clays is developed, after which there follows the Paleozoic mass of rocks, which, at the total borehole depth of 363 m, was penetrated for 329 m and, by lithological composition, may be divided into two parts.

The upper half, developed to a depth of 304 m from the surface, according to Prof. V. A. Obruchev, who in 1901 personally examined the borehole cores, is characterized by the development of limestones, more or less dolomitized, “now softer, now harder, with interbeds and pockets of black flint, and in places also of sulfur pyrites” (48). To this it should be added that the limestones here have various, most often light, shades of gray, are sometimes distinguished by a “resinous” odor (Nos. 9, 14 of the section), having a bituminous character, and are often silicified. In addition, in the upper and especially in the lower part they are sometimes distinguished by a brown or dark-brown coloration. Such are beds Nos. 21, 74, 75, and 76 of the above section of the Almaznaya borehole, of which the last three occur at a depth of 163 m from the beginning of the Paleozoic and form a horizon of brown limestones 18 m thick. Finally, in the same section attention is drawn to the numerous traces of tectonic displacements and folding of the rocks, considered above.

In other deep boreholes, owing to drilling conditions, the coloration and bituminous character of the rocks find better expression in the mass under consideration. Thus, for example, in borehole No. 1 the upper 80 m are composed of bituminous limestones; and in the Maltinskaya borehole, in the upper half, a light coloration is noted, and in the lower half a dark-gray or even black one; moreover, the latter varieties of the rock are distinguished by bituminous character—which entirely agrees with the data cited above from direct observations of limestone outcrops along the Belaya River.

A somewhat special position is occupied by the section of the Brodovich borehole, where, beginning at a depth of 20 m, limestone with cracks and cavities filled with clays begins, up to 40 m thick; below lies a dark-gray hornstone with sulfur pyrites—11 m, and then a light-gray calcareous rubble with inclusions of gypsum, more than 30 m thick. This section is not correlated with any borehole and is evidently explained by the fact that the Brodovich borehole, in the first hundred meters, intersected a strip of limestones that had been crumpled and displaced by upthrows, as was noted above and shown in Fig. 15. Below the zone of disturbances there are already normal limestones, which are then replaced by beds of clays and argillaceous shales of small thickness, underlain, finally, by red sandstones at a depth of 190 m (183 m from the beginning of the Paleozoic). Unfortunately, at this depth the borehole stopped, at the time causing perplexity over the section obtained in it. In this section, special attention was attracted by the red sandstones, established at a comparatively shallow depth and not encountered at all in the Almaznaya borehole. And, since within the Irkutsk Paleozoic these rocks were known at the base of the entire thick limestone mass, where they compose the Motskaya red-colored suite, then, in connection with the above-mentioned signs of obvious disturbance, all this gave grounds to think of a large upthrow that had brought these rocks from a great depth to the 190 m horizon (1). But the new deep boreholes drilled in recent years to a certain extent dispelled this puzzle, since the same sandstones and, below them, again a limestone mass were encountered at a depth of 162 m in borehole No. 2, which here gave the following sequence of beds:

1. Red-brown calcareous sandstone . . . 3 m.
2. Calcareous-argillaceous shale . . . . . . 3 m.
3. Red-brown calcareous sandstone . . . 3.7 m.

1. Calcareous clay shale . . . . . . 5.5 m.
2. Red-brown calcareous sandstone . . . 3 m.
3. Calcareous-clayey shale . . . . . . 21 m.
4. Limestone . . . . . . . . . . . . . —

In this section, it is true, as also in the section of the Brodovitsa borehole, it is difficult to regard the determinations of the rocks with complete confidence, in particular the expression “red sandstone.” Under the working conditions here, errors were possible. But the recurrence of one and the same rock at nearby horizons in two different boreholes, moreover drilled at different times and by different persons, already makes its presence probable; and this is all the more so because the possibility of thin interbeds of red sandstone at the indicated depth is not in contradiction with other facts, in particular with the data of the Diamond borehole. The red coloration of the rocks is also quite consistent with the section of the latter, since at a depth of 163–181 m from the beginning of the Paleozoic, as was indicated above, a horizon of brown limestones was established in it. It is interesting that, within the same depth (192 m from the beginning of the Paleozoic), dark-brown clays 32 m thick were also noted in the section of the Maltinskaya borehole.

Thus, the rock sequence of the Usolye Paleozoic considered here is characterized by the development of marly, more or less dolomitized and silicified limestones, often bituminous both in the upper and especially in the lower part, and therefore it may be distinguished under the name of the marly and bituminous horizons¹.

To what has been said it should also be added that, in the marly limestones exposed at Limestone Cape, in the summer of 1925 I found a fragment of an impression of the head shield of a trilobite close to the genus Olenoides. This find somewhat strengthens the parallelization we are making of the limestone sequence of Usolye with the limestones of the Cheremkhovo district, since in the latter, in 1923–1925, in the vicinity of the Cheremkhovo mines and along the B. Belaya River near the village of Belsk, I found a quite determinable, though small, trilobite fauna of the Olenoides group, now already studied by E. V. Lermontova, who assigned it to the Middle Cambrian (40; 81). With the tectonic relationships clarified above and with the great lithological similarity of the limestones of the Usolye and Cheremkhovo districts, all this gives grounds to refer the described Usolye horizons also to the same middle division of the Cambrian system.

From a depth of 304 m below the surface and 270 m from the beginning of the Paleozoic, a new rock sequence is naturally distinguished in the Diamond borehole. Its essential distinguishing feature is, on the one hand, the development of a large number of gypsum interbeds and, on the other, of layers of clays and clayey shales significant both in number and in thickness.

Interbeds of gypsum, when their thickness is small, are, understandably, difficult for Kleist’s drill to detect; therefore the best expression of the first half of the section is again found in the Diamond borehole. From a depth of 304 m, over an interval of 35 m vertically (Nos. 94–109), two rather thick beds of gypsum (Nos. 94 and 99) are recorded here, each of which reaches almost 1 m, as well as a large number of thin interbeds. Among the other boreholes, of greatest interest in the same respect is the Maltinskaya, where from a depth of 247 m the following were passed through:

1. White tuffaceous limestones with a coating of gypsum . . . . . . 18.29 m.
2. Dark-blue calcareous clay . . . . . . . . . . . . . . . . . . 9.64 »
3. Gypsum . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.05 »
4. Limestone with interbeds of gypsum . . . . . . . . . . . . . . 4.25 »

1. Limestone . . . . . . . . . . . . . . . . . . . . . . 3.96 m.
2. Dark-blue clayey shale . . . . . . . . . . . . . . . 25.67 »
3. Limestone with interbeds of gypsum . . . . . . . . . 4.20 »

In the sections of the other deep boreholes, gypsum-bearing character is either not recorded at all, or finds only weak expression, as, for example, in borehole No. 3, where at a depth of 293 m there is indicated “limestone with interlayers of clayey shale and grains of gypsum.”

As regards the other feature of the horizons under consideration noted above, namely the substantial participation in their composition of clays, clayey shales, and clayey limestones, it is well expressed in almost all the boreholes.

Thus, in borehole No. 2, from a depth of 221 m down to a depth of 305 m, there occur chiefly clays and clayey shales, giving a total thickness of 58 m; and alongside them clayey limestones are developed, making up 26 m in all. The development of clays and numerous interbeds of clayey shale in the limestones was also established in borehole No. 3, and especially in the Malta borehole, where, at a depth from 260 to 380 m, we find five rather thick beds of clays and clayey shales, giving a total thickness of 61 m. A weaker participation of clayey rocks in the composition of these horizons is expressed in the section of borehole No. 1, where, however, from a depth of 233 m there is nevertheless indicated a series of small beds of clays and clayey shales and thin shale interbeds in the limestones. In the Almaznaya borehole, however, which reached a depth of 362 m (328 m from the beginning of the Paleozoic), this lithological element found no reflection whatever.

However, there is no reason to think that the absence of clayey horizons in the section of the Almaznaya borehole can indicate the possibility of a general error in all the other boreholes. Apart from the concordant indications of the sections of all the boreholes, their presence is confirmed by the development of an aquifer associated with them, occupying, moreover, the same isolated position, as may be judged from analyses of the waters¹). Hence follows the following, quite possible interpretation of the section of the Almaznaya borehole: the clayey horizons could not enter the section of this borehole for the reason that they evidently lie below the depth of 362 m at which it stopped. It is very probable, moreover, that these horizons are very close to, or even directly follow after, the bottom of the borehole, since the lower part of its given section bears evident signs of an aquifer developed here, the water-resistant bed of which must be the clays and clayey shales lying below. These signs may be discerned in those numerous beds and interbeds of gypsum which were considered above, and by which this part of the section of the Almaznaya borehole is naturally connected with the underlying clayey horizons.

Thus, this new thickness is characterized by a substantial participation in its composition of clays, clayey shales, and clayey limestones, and, with the understandable development of an aquifer in connection with them, is further distinguished by the presence of gypsum. In view of the possible secondary origin of the latter, we distinguish this new thickness under the name of clayey-limestone horizons²).

¹) This is discussed in greater detail in the following chapters.

²) The secondary origin of the gypsum, very possible under conditions of circulation of salt solutions above clayey horizons, makes it most probable that it occurs not in beds or interbeds, as indicated in the boreholes, but rather in irregular nests and lenses formed when gypsum-filled voids from the leaching of limestone by underground waters were filled. The development, within the described horizons, of such a process is indicated, for example, by the above-mentioned “tuff-like” character of the limestones in the Malta borehole. With such an interpretation, the gypsum-bearing character could be regarded as a phenomenon of a purely local character. However, we have data on the broad horizontal distribution of this feature of the horizons considered: it is also preserved in the foothills of the Eastern Sayan, for example, in the area of the village of Moty—Bodary. Considering as most probable only the view of the gypsum-bearing character of these horizons set forth here, we therefore admit the possibility also of a primary

The above-described beds of the Usolye Paleozoic contain rather varied lithological components. This diversity may serve as a basis for distinguishing individual horizons; but at the same time it is a characteristic feature of the entire sequence, as an expression of the instability of the physiographic conditions of the Middle Cambrian sea. Therefore we combine all these horizons into a single Usolye stage, having a thickness from 300 m (boreholes Nos. 1, 2, and 3) to 370 m (the Malta and, probably, Almaznaya boreholes), and dividing into two groups of horizons: above occur marly and bituminous limestones, often dolomitized and silicified, with a thickness from 150 m (Brodovich’s borehole) to 270 m (Almaznaya borehole); and below are developed limestone-clayey horizons, in the upper part noticeably gypsiferous, whose thickness ranges from 80 to 150 m. The thickness and depth of occurrence of these horizons in the sections of individual boreholes are shown in Fig. 17.

From a depth of 300–315 m in boreholes Nos. 1, 2, and 3, and about 370 m in the Malta borehole, begins the second stage, which continues down to the salt-bearing sequence, i.e., to a depth of 690 m in boreholes No. 1 and No. 3, having, consequently, a thickness of 375–390 m. This stage, penetrated completely only by boreholes No. 1 and No. 3, is characterized by a composition of a more or less homogeneous mass of limestones, only rarely, especially in the upper part, interbedded with clays and clayey shales, which here already occupy a quite subordinate position.

The work of deepening borehole No. 3, carried out in the summer of 1925, gave me the opportunity to acquaint myself with drill samples of the limestones of this stage at depths from 420 to 550 m; their composition confirms its uniformity. The samples are represented by monotonous gray limestones, noticeably marly, sometimes with small fragments of chert; nodules and very small fragments of gypsum occur in them only rarely; and only in samples from about 520–530 m is there found, together with the same limestone, fine shingle of dark-gray clayey shale. The indicated composition of the rocks gives grounds for assigning to it the name “stage of gray marly limestones.” Its age, most probably, is also Middle Cambrian.

At about 700 m depth from the surface begins the last “Salt-bearing stage,” about which we as yet have incomplete information, since borehole No. 1 only cut into it and, having passed about 30 m, stopped because of a break in the cable; while borehole No. 3 passed 75 m through the salt-bearing sequence, stopping in February 1926 because of a lack of equipment and funds for further deepening.

In view of the special interest of this stage, an extract from the drilling log of borehole No. 1 is given below in full, providing an idea of the composition of its upper half¹. Beneath the limestones, at a depth of 692 m, follows²:

1. Rock salt of grayish-white color . . . . . . . . . . 3 m.
2. Dark-gray, almost black, resinous marl . . . . . . . 0.3 »

of gypsum origin—which may also be indicated by the large number of gypsum interbeds, as well as by the considerable thickness of some of them, reaching up to 1 m.

A somewhat special position in the composition of the horizons considered is occupied by the blue clays that are indicated in the Malta borehole. The blue coloration in clays is usually due to the presence of finely dispersed ferrous iron in the form of melnikovite, developing both in shallow-water and sometimes in deep-water marine and lake basins, especially under conditions of accumulation of organic matter that reduces sulfates (29; 3,37). In particular, the Cambrian blue clays of Leningrad Governorate, according to the investigation of Acad. Fersman, owe their color to finely distributed pyrite and glavconite, and were formed under conditions of a shallow sea (30; 119).

1. Rock salt of reddish-gray color, gradually changing
   to pink, with small particles of shaly clay . . . . . 4.8 m.
2. Rock salt, light gray, below with brown bituminous
   mud . . . . . . . . . . . . . . . . . . . . . . . . 9.3 »
3. Resinous dolomite . . . . . . . . . . . . . . . . . 0.9 »
4. Resinous rock salt, with thin interbeds of dolomite . . 0.4 »
5. The same, with interbeds up to \(1/2\) f. thick of bluish plastic
   clay with flint . . . . . . . . . . . . . . . . . . . 1.1 »
6. The same, with interbeds of dark clay . . . . . . . . 2.4 »
7. The same, with interbeds of gray clay . . . . . . . . 2.5 »
8. The same, with interbeds of dolomite and gypsum . . . 0.6 »
9. Fine-grained rock salt with interbeds of resinous
   dolomite . . . . . . . . . . . . . . . . . . . . . . 0.9 »
10. Coarse-grained rock salt . . . . . . . . . . . . . . 0.6 »
11. Fine-grained rock salt with interbeds of light dolomite . 0.9 »
12. Fine-grained rock salt with interbeds of dolomite and clay . 0.9 »
13. Coarse-grained rock salt, yellowish-brown in the sample, in
    individual fragments colorless and transparent . . . . 2.4 »
14. The same, with interbeds of shaly clay, dolomite, and gypsum . 1.2 »
15. Rock salt with interbeds of gray hard shaly clay . . . 3.3 »

This upper part of the salt-bearing thickness in borehole No. 3, complex in composition, for the reason stated above has been reduced to a single bed of rock salt. But lower down, the drilling of this borehole was carried out under the supervision of mining engineer A. S. Golovenkov, who gave a fairly detailed section of the second half of the stage as well. The salt-bearing deposits here begin at a depth of 690.9 meters, where beneath the limestones there follows (49):

1. Gray salt with interbeds of clay . . . . . . . . . . . 0.5 m
2. Salt . . . . . . . . . . . . . . . . . . . . . . . . 1.0 »
3. Hard salt . . . . . . . . . . . . . . . . . . . . . 33.1 »
4. Hard salt . . . . . . . . . . . . . . . . . . . . . 1.3 »
5. Soft white salt . . . . . . . . . . . . . . . . . . 0.9 »
6. Hard salt . . . . . . . . . . . . . . . . . . . . . 2.3 »
7. Soft salt with a large amount of clay . . . . . . . . 1.4 »
8. Soft salt, purer . . . . . . . . . . . . . . . . . . 1.0 »
9. Soft salt, pure, white . . . . . . . . . . . . . . . 1.1 »
10. Hard salt . . . . . . . . . . . . . . . . . . . . . 6.7 »
11. Soft, clayey salt . . . . . . . . . . . . . . . . . 0.5 »
12. Marl . . . . . . . . . . . . . . . . . . . . . . . 1.3 »
13. Quartz–mica sandstone . . . . . . . . . . . . . . . 0.6 »
14. Gray salt . . . . . . . . . . . . . . . . . . . . . 0.3 »
15. Gray, clayey salt . . . . . . . . . . . . . . . . . 0.5 »
16. Clay shale with siliceous concretions . . . . . . . . 4.85 »
17. Clay shale with rock salt . . . . . . . . . . . . . 0.7 »
18. Clayey rock salt . . . . . . . . . . . . . . . . . 0.5 »
19. Strongly clayey salt . . . . . . . . . . . . . . . 0.7 »
20. Clay shale . . . . . . . . . . . . . . . . . . . . 1.3 »
21. Clay shale with thin interbeds of rock salt . . . . . 0.9 »
22. Clay shale . . . . . . . . . . . . . . . . . . . . 2.0 »
23. Gray rock salt . . . . . . . . . . . . . . . . . . 2.0 »
24. The same with hard clay shale . . . . . . . . . . . 3.1 »
25. Rock salt and siliceous concretions in clay shale . . 0.4 »
26. Clay shale with thin interbeds of rock salt . . . . . 0.9 »
27. Clay shale . . . . . . . . . . . . . . . . . . . . 0.9 »

The salt-bearing deposits penetrated by borehole No. 3 hardly encompass the full composition of the third tier, which probably has a much greater thickness. Nevertheless, even what is now known about it already gives an idea of the structure and of certain properties of this most important stratigraphic element in the geology of the deposit, namely:

With a total known thickness of the tier of 70.75 m, the useful thickness of rock salt reaches 57.3 m—which, however, is somewhat exaggerated, since in the very upper part of the section (borehole No. 1, beds 1–17), and partly in the lower part, the salt is often clayey and interbedded with numerous thin partings of clay and clayey shale, which cannot be taken into account. In addition, the lower part of the section includes several beds of clayey shales with thin interbeds of rock salt, giving a total of 2.5 m. The thickness of the few interbeds of barren rock in the form of clayey shales without signs of salt reaches only 10.96 meters. Such a composition of the salt-bearing deposits makes it possible to say that here we have, in essence, one thick and complex bed of rock salt. But, according to the varying purity of the useful mineral and the different participation in the composition of the bed of interbeds of barren rock, it may be divided into two unequal parts.

The upper part of the bed comprises beds 1–11 of the above section of borehole No. 3, has a thickness of 49.8 m, and may be characterized as a continuous deposit of salt, more or less contaminated by very thin interbeds of rock in the form of clay, dolomite, and, more rarely, gypsum, as is shown in the section of borehole No. 1, which cut this part of the bed for 32 meters. This latter section must, of course, be treated with some caution, since, in the opinion of mining engineer A. I. Sosov, who observed the drilling of the borehole, the contamination of all salt samples must to a certain extent be explained by drill cuttings from the upper horizons inevitably remaining in the brine-filled borehole. But alongside this, A. I. Sosov, in a note in the log, draws attention to the presence in the samples of fairly large fragments of crushed rocks—which may indicate the actual complexity of the bed’s composition. The same is confirmed by the drilling foreman, the American subject Evans, under whose supervision almost all the deep boreholes of Usolye were sunk. He points to the uneven operation of the tool when passing through the bed, which is usually observed when hard and softer rocks alternate. It may therefore be thought that the reports of the complex composition of the upper deposit of rock salt deserve confidence. It may also be suspected that the part of the deposit comprising, in the above section of borehole No. 3, beds Nos. 4–11, which showed the same alternation of hard and soft interbeds, is distinguished by a similar composition. To what has been said one may add further that the interbeds of rock and the salt itself differ in various shades—sometimes brown, red, and pink, but more often gray and black.

As for the lower half of the salt bed, it amounts to only 20.2 meters, is already distinguished by a sharply expressed heterogeneity of composition and by a considerably lower salinity, which gradually decreases downward. Pure rock salt is represented here by only two beds with a thickness of 2.3 m; two new beds of 1 m give clayey salt; 6 m consist of beds of clayey shales with rock salt; and 10.9 m fall to barren rock without signs of salt. It is characteristic that the interbeds of barren rock are represented almost exclusively by clayey shales, and some of them are distinguished by considerable thickness. For example, bed No. 16 of borehole No. 3 reaches almost 5 meters, while the following beds below, Nos. 20, 21, and 22, of clayey shales together make up 4.2 m. This feature of the composition of the lower horizons of the salt-bearing deposits compels one to see in them the impervious bed of underground waters circulating in the mass of the upper salt deposit. This latter circumstance provides an expla—

... and also by that peculiarity of the given deposit that in none of the sections of the deep boreholes has anhydrite, so characteristic of salt deposits, been recorded in the composition of this stage: under conditions of underground circulation of waters and the associated phenomenon of hydration, the anhydrite probably turned into gypsum, established in the composition of the upper salt bed of borehole No. 1 (see beds Nos. 10 and 16).

Thus, the salt-bearing series exposed by the deep boreholes is represented, in its upper part, by a continuous bed of rock salt, more or less contaminated by thin interbeds of rocks and reaching a thickness of almost 50 m; and in the lower part, chiefly by beds of clayey shales, either pure or more or less salt-bearing, and by a small number of rock-salt beds of insignificant thickness.

Thus, the composition of the Usolye Paleozoic may be reduced to the following three stages:

1. Marly and bituminous limestones, gray and dark gray, below replaced not infrequently by a thin alternation of limestones, clays, and clayey shales, with a thickness of . . . . . . . . 300–370 m.

2. Gray, uniform, more or less marly limestones . . . . . . . . . . . . . . . . . . . . . . 375–390 m.

3. A salt-bearing series in the form of a bed of rock salt, interbedded with clays and clayey shales . . . . . . . . more than 74 m.

The stratigraphic composition of the Usolye Paleozoic derived above, in connection with the different hypsometric position of the same stages and of the horizons composing them in different boreholes, shown in Fig. 17, opens the possibility of certain additions to the scheme of the tectonic structure of the deposit given in the preceding chapter, especially with regard to the question of the type and scale of the principal disturbance passing near the Almaznaya, Brodovich, and No. 2 boreholes.

In Fig. No. 15 a scheme of the tectonics of the deposit was given, at which we arrived chiefly on the basis of the study of the surface, both in the area of the deposit itself and in other parts of Irkutsk Province, and which outlines only the general prevailing type of disturbances. Fig. 17, together with the sections of the deep boreholes, gives an attempt at reconstructing the main zone of the Usolye disturbances, based on the above analysis of the stratigraphy of the Usolye deposit and, in particular, on the very probable deep position inferred for the limestone-clayey horizons in the Almaznaya borehole, where they should lie almost 150 m lower than in boreholes No. 2 and Brodovich. If such an almost sudden and deep sinking of the named horizons is admitted here, one may assume a fairly large disturbance, the type of which cannot be established without additional exploration; and therefore we outline here two possible variants (in Fig. 17 A and B).

The first variant assumes a rather large reverse fault, in the deep horizons associated with boreholes Nos. 1 and 3—this is indicated by the sharp jump in the strength of the brines from 6° and 6.5° B. to 16° and 18° B. in both boreholes—and, nearer the surface, by a whole bundle of reverse faults of the second order, which include the Almaznaya, Brodovich, and No. 2 boreholes and produce a series of disturbances and cracks at the surface, with which many salt springs are associated. The second variant assumes a simpler form of disturbance in the form of a large flexure, with which a series of lighter movements nearer the surface may likewise be connected. Both of these variants seem to us entirely possible. It should nevertheless be noted that the Ponomarevskaya, which comes out at the surface,

the flexure on the Angara River, mentioned in the geological sketch of the Cheremkhovo district, is accompanied by a large number of small disturbances of the second order, chiefly in the form of small pillar-shaped folds and thrusts, whereas in the environs of the Usolye deposit typical upthrows are encountered. This gives us some grounds for considering the first variant the more probable.

In any case, the admission of both variants gives a satisfactory explanation of a whole series of phenomena in the Usolye deposit that otherwise are insufficiently intelligible, namely: 1) The increase in the thickness of the clayey horizons in the direction of Bredovich’s borehole is easily explained by the dragging of clays during bed-parallel displacements in the direction of the axis of the main disturbance—something which, incidentally, is very often observed on a small scale in the Cheremkhovo district (19). 2) The broken horizons of rocks at depths of 100–150 m in the Almaznaya borehole and at depths of 50–100 m in Bredovich’s borehole find their explanation in very probable movements of the second order. 3) The same disturbances of the second order must explain the large number of fissures and the associated outlets of saline springs in the park of the Usolye resort and in the upper part of Varnichny Island. 4) With the probable intersection by one of such movements of the very upper horizons of the Almaznaya borehole one may also connect the great thickness, established by this borehole, of breccia-like conglomerate above the Paleozoic limestones, which, especially in its lower half, is better assigned to the category of tectonites, like the “limestone rubble” in Bredovich’s borehole. 5) The highly probable vigorous circulation of groundwater, in connection with the numerous tectonic fissures of the same Almaznaya borehole, which passed through the zone of greatest compression of the main disturbance, makes understandable the strong silicification of the limestones penetrated by it, unknown to such a degree in other places. 6) The intersection of the main zone of disturbance by borehole No. 2 explains the very great thickness of the limestone-clay horizon traversed here, especially at a depth of about 300 m, where a fine interbedding of clays and clayey limestones is observed, and where one may suppose the passage of the main fissure. 7) Under the conditions outlined, the high yield and considerable strength of the brine in borehole No. 2, and especially in Bredovich’s borehole, are also intelligible—features not known at shallow depths in the other boreholes. The strength of the brine in these boreholes is, it is true, much lower than the strength yielded by boreholes Nos. 1 and 3 when they intersect the main fissure of the upthrow. But this is readily explained by dilution of the brine by waters of the upper horizons, as well as by the possible partial plugging of the fissure itself by clay—something very probable where it crosses a clayey horizon. 8) Finally, the inferred disturbances may also give a satisfactory explanation of the phenomenon of the greatest head of water in the Almaznaya borehole, since the position of the latter in the immediate vicinity of the face of the main disturbance connects it, more than any of the other boreholes, with a very large number of tectonic fissures, each of which may give a considerable increase in head—as will be discussed in greater detail below.¹

¹ In the tectonic scheme outlined in Fig. 17, the relative distribution of the deep boreholes requires explanation, since it differs from that given in Fig. 11 and was obtained under the assumption that the tectonic fissures are oriented at an azimuth of 47°. Acceptance of this azimuth for the present case, while preserving in the scheme of Fig. 17 the former position of the Almaznaya borehole between Bredovich’s borehole and No. 2, would have led us to an improbable tectonic form in the shape of a rather deep graben or a compressed deep fold. Therefore we allow here another, quite possible—and, for the disturbances we have noted, more probable—azimuth of 60°–62°, along which, or close to which, many joints and some disturbances are often oriented in our district. Acceptance of this azimuth, which is fully admissible according to the data of actual observations, also caused a slight displacement of the Almaznaya borehole, which appears in the scheme of Fig. 17 to the SE of Bredovich’s borehole.

Position of the Usolye Paleozoic in the General Stratigraphic Scheme of the Irkutsk Amphitheater

According to the investigations of Prof. V. A. Obruchev (9) and A. Rzhonsnitskii (14; 15), as well as to the more recent summaries by V. A. Obruchev (26; 40) and M. M. Tetyaev (31), the Lower Paleozoic of the Irkutsk Amphitheater is represented by Cambrian and Silurian deposits; moreover, within its southern margin, in the Irkutsk coal basin, only the Cambrian is developed. The sediments of this system are widely developed here and are represented by all three of its divisions. In the Lower Cambrian, during which, according to Obruchev’s scheme of geological cycles of Zonneder, the continental phase predominated, we find a thickness of red-colored rocks; in the middle division, corresponding to the phase of submergence, there is a rather thick series of limestones, associated with the lower division by a transitional stage of red-colored, gypsum- and salt-bearing rocks; with the same series of red-colored rocks we also encounter the upper division, during which the phase of the alternating state took place.

The Paleozoic series of the town of Usolye described above, at least in its first two stages, must evidently be assigned to the Middle Cambrian, as we have done above on the basis of lithological and partly faunistic data. As for the third, Salt-bearing stage, it may occupy the position of the lower stage of the Middle Cambrian (40; 80), or enter into the composition of the lower division of the system.

Certain additions to this general scheme are introduced by later observations in Irkutsk Governorate, in particular in the vicinity of the village of Moty—Bodary, in the upper system of the M. Iret River, at a distance of about 70 km to the southwest of Usolye, where in 1925 I made a week-long excursion in connection with the study of the stratigraphy of the Usolye district. In a few words, the data of these observations amount to the following.

Directly opposite the village of Moty, on the right bank of the M. Iret River, rises Mt. Bodara, reaching a height of 300 m above the level of the valley and, throughout its height, composed of Paleozoic, evidently Middle Cambrian, limestones. But at the foot of this mountain, from beneath the limestones there emerges a red-colored series of Moty sandstones, which, according to earlier investigations (10; 253) and the most recent observations of M. M. Tetyaev (21; 656), already overlie the pre-Cambrian crystalline suite and must be assigned to the Lower Cambrian (40; 65). Thus before us here appears a red-colored series of the Lower Cambrian and the lower and higher horizons of Middle Cambrian limestones covering it, which in the Usolye district lie at very great depth. The understandable, and therefore great, interest of the rock composition in the environs of the village of Moty prompted me, during the above-mentioned excursion, to attempt to compile a section of Mt. Bodara. It must be said that the slopes of this mountain are strongly turfed; on the northern slope outliers are even rare, and only the very steep southern slope gives a few isolated exposures and a very large number of outliers, to which, given the presence of several terraces on the slope, a certain significance may also be attached. Of course, the section I obtained under these conditions represents only a rough approximation to reality. But on the scale of the stratigraphy of the Usolye Paleozoic outlined by us, it acquires considerable interest. This section has the following composition in descending order¹.

1. Gray, dense, partly silicified limestone, medium-platy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . thickness 50 m.

Terrace.

1. Light-gray, distinctly granular limestone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 m.

2. Limestone, dark gray, sometimes almost black, bituminous, now medium-, now fine-grained, always very hard . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 m.

3. Gray granular limestone, porous and strongly cavernous, often as if corroded, with gypsum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 m.

4. Below it, alternating with it and gradually replacing it, is a yellowish-gray spotted limestone, dolomitized, granular and often crumbling, forming a series of small cliffs and enormous detached blocks—boulders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 m.

Flat terrace.

1. Gray coarse-grained quartz, sometimes conglomeratic sandstone, rapidly passing into brick-red banded sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 m.

Level of the Kamykhta River.

Total . . . . . . . 300 m.

In this section it is easy to find almost all the horizons of the Usolye Paleozoic. Thus, nos. 1–3, fully corresponding to the section along the B. Belaya River given on p. 25, must be assigned to the horizon of marly and bituminous limestones of the Usolye stage. The lower horizons of the same stage may be discerned in the development of gypsum and the strong corrosion of the limestones of no. 4, which at the same time permits one to assume the strong water-bearing character of this horizon and the occurrence, close to it, of clayey beds not recorded in the scheme presented, because of the heavily turf-covered slopes of Mt. Bodara.

The characteristic spotted and crumbling limestones of no. 5 must already be assigned to the second stage, which may be called the Bodara stage. As for, finally, the Saliferous stage of Usolye, it finds no other expression on Mt. Bodara except no. 6 of the section, where coarse-grained, sometimes conglomeratic sandstones crop out, which then pass into the reddish Moty suite; this latter, however, may be regarded as a formation of the same order as the saliferous deposits.

However, between the given Cambrian sections there is also a substantial difference, namely: in the first stage of Mt. Bodara the very upper beds, in the form of thin-platy marly limestones 40 m thick (nos. 1 and 2 of the section of the B. Belaya River), are lacking—which is easily explained by their weathering and erosion. Also characteristic is the comparatively small thickness of the Middle Cambrian, which in the section presented amounts to only 285 m instead of 700 m in the area of the town of Usolye.¹ This difference appears still more sharply if one takes into account the slight discrepancy in the composition and thickness of the preserved part of the Usolye stage—which compels one to assign the difference entirely to the account of the second Bodara stage, which gives about 400 m at Usolye and only 100 m on Mt. Bodara. This circumstance may find various explanations; but it is, in any case, quite possible in peripheral regions of such a mobile zone of the lithosphere as, at the very beginning of the Paleozoic, was probably the contemporary mountain system of the Western Sayan.

Finally, the different lithological expression of the third stage—represented in the town of Usolye by salt-bearing horizons, and in the town of Bodary by a varicolored sandstone sequence—does not in the least prevent them from being recognized as synchronous formations, given the entirely admissible closeness of the physiographic conditions of their sedimentation.

The observations cited above in the vicinity of the village of Moty-Bodary, and the possible correlations of the Paleozoic developed there with the Usolye section, lead us to the conclusion that both the varicolored sequence of the Moty sandstones and the salt-bearing stage of the town of Usolye, synchronous with it, belong to the Lower Cambrian; and that, within the Middle Cambrian, two stages are distinguished in both sections: the lower, Bodary stage, highly variable in thickness and composition, and the upper, Usolye stage, distinguished by constancy of composition and thickness.

This stratigraphic scheme may receive further refinement as a result of my latest observations along the northern margin of the Irkutsk coal basin, in Balagansk District, and on the Oka–Iya watershed. According to these data (34; 33), the gypsum-bearing Balagansk stage, separated by K. I. Bogdanovich (10) into an independent stratigraphic unit overlying the Middle Cambrian limestones, is, in its lower half, merely a facies change of the horizon of marly limestones with which the Usolye stage of the Middle Cambrian begins. The gypsum-bearing Balagansk suite is, moreover, overlain by a sequence of light-gray and white quartz sandstones of the Oka suite, which may already be assigned to the Upper Cambrian, since on the Oka–Iya watershed in 1926 there was established within it a horizon of glauconitic calcareous sandstones with an obolid fauna (Obolus, Linguella), very probably of Upper Cambrian age. Thus the Balagansk gypsum-bearing suite, together with the marly limestones of the Usolye stage, may occupy the stratigraphic position of the upper horizons of the Middle Cambrian.

Of course, all the stratigraphic constructions underlying the volume of the Usolye Paleozoic adopted here are based on paleontological material that is still insufficient; with the accumulation of such material, they may undergo certain changes. The glauconitic sandstones with an obolid fauna may occupy, for example, a place in the very lowest horizons of the Silurian. In that case the Usolye Paleozoic would end with the Middle Cambrian, and the upper half of the Balagansk suite, eroded away in the Usolye area, would take the place of the Upper Cambrian.

In connection with the analysis of the stratigraphic composition of the deposit, the question always arises also of the horizontal extent of at least the productive horizons of the sequence under study. This question is directly connected with the facies changes of the Irkutsk Cambrian, as well as with the question of the elements of ancient tectonics, and in the geology of the Usolye deposit, it may be said, has not yet been touched upon at all by investigators. It is understandable, therefore, that we are deprived of the possibility of even approximately outlining the area of distribution of the salt-bearing deposits. We can only state the very wide distribution of salt springs and the associated salt marshes, which from the system of the Belaya River and its upper tributaries, the Golumeti and the Alar, through the area of Malta station of the Tomsk Railway, pass into the vicinity of the town of Usolye and continue farther north, to the headwaters of the Ilim and Lena rivers. As for delineating the salt-bearing area, this will become possible only when the stratigraphy, as well as the Cambrian tectonics and, in connection with this, the facies changes of the divisions of this system, have been more fully studied. At present, on the basis of only two deep boreholes that have reached the salt-bearing stage, it can only be said that the rock-salt deposit has a probable useful area of not less than one square kilometer, and that the probable reserves of rock salt in it reach 140 million tons.

Groundwater and Springs

The description of the stratigraphic composition and tectonics of the deposit provides a basis for judging the groundwater of the region, its distribution in the vertical and horizontal planes, and the conditions under which it emerges at the surface in the form of springs.

Within the three formations characterized in the Usolye district, one may speak of five aquifer horizons. The first aquifer horizon from the surface, corresponding to the concept of groundwater, is often associated with the modern deposits of the Angara River, which, in addition to sands and gravels distinguished by the best water-bearing capacity, were shown to contain clays, which here play the role of the impermeable bed of the horizon. This horizon, however, can have only a very limited horizontal extent, since the modern deposits in our district are connected only with river valleys and, chiefly, with the valley of the Angara River; moreover, impermeable clays are not a constant member in their composition. It is quite understandable that its significance is not very great, especially since the thickness of the clays overlying the sands and gravels usually does not exceed two or three meters. Of much more serious importance in our deposit is another hydrogeological role of the modern deposits of the Angara River. Where these deposits occur directly on the Paleozoic, their role is often reduced to clogging and, not infrequently, to complete plugging of tectonic fissures and the associated artesian salt springs. In other cases they cause the dispersion and dilution of saline waters, thus masking or altogether destroying the surface expression of the salinity of the given area.

Much greater significance belongs to the second aquifer horizon, associated with the lower beds of the Jurassic deposits. Given the limited horizontal extent of the first, this horizon in many cases also collects groundwater. It is characterized by a considerable thickness of its impermeable bed in the form of clays and argillites, reaching up to 10 m, by the great persistence of the latter, and by the excellent water-bearing capacity of the overlying Jurassic sandstones; it occurs at varying, sometimes rather great depths and therefore, understandably, is of very great importance in Irkutsk Governorate, being the chief reservoir of drinking water for the population. It also plays a noticeable role in the Usolye district, where it must likewise have a considerable extent, especially in the southern half—for example, on Spassky Island, as well as throughout the southern part of the town itself. It may also be of great importance in the distribution of ascending waters from the deep horizons. But within the Jurassic coal-bearing formation there may also be a number of further aquifer horizons. However, according to data from the deep Barkhatovskaya borehole (19;18), they may occur at a level exceeding the horizon just considered by only about 70 m, i.e., they are associated with that part of the Jurassic which in the Usolye area has been eroded and cannot have practical significance.

In the Cambrian rock mass we identify three aquifer horizons. The first most often lies at a depth of about 200 m, having at its base the limestone-clayey horizons of the Usolye stage, and as aquiferous beds the overlying mass of limestones, to a considerable degree bituminous. In Usolye this horizon, understandably, is established only by deep boreholes. But in places it also reaches the land surface—something observed only in high anticlinal uplifts, for example along the Bolshaya Belaya River, in the Bel’sk–Kholmushino sector, and especially in the area of the village of Bel’sk, where a large number of strong springs and phenomena of waterlogging are associated with it. With its great depth of occurrence and the considerable number of limestone clays and clayey shales underlying it—often, it is true, not very thick—this horizon must be distinguished by a wide distribution. The previously noted ...

the texture of the bituminous limestones that come to the surface along the Belaya River and that are always distinguished by a clearly granular composition, porosity, and sometimes coarse cellularity, makes it possible to assume a high degree of water-bearing capacity in them and, at the same time, a considerable saturation with the waters of this horizon. The latter circumstance, in connection with the comparatively easy accessibility of depths down to 200 m, makes it very important in the region, especially with respect to the collection of waters arriving from deep horizons. The regime of the waters of deep wells described in the following chapter, the changes with depth in the strength of the brines, as well as the different chemical composition of the waters of these depths, always more or less sulfurous, fully confirm the independence and important significance of this water-bearing horizon.

The thick Bodarinian stage of the Middle Cambrian, developed to a depth of about 700 m, can hardly contain water-bearing horizons, since neither of the two deep wells that penetrated it revealed in its composition any appreciable beds of clay or argillaceous shales. But the composition of the underlying Salt-bearing stage of the Lower Cambrian, in which clays and argillaceous shales play an essential role, and the salt itself is often clayey, leaves no doubt as to the presence of water-bearing horizons in it. It is most probable that here we have two more or less independent horizons, as required by the clayey character of the salt deposit from its uppermost layers and by a series of appreciable beds of clay and argillaceous shales in the lower half. This is confirmed by the high strength of the brine in the deep tectonic fissures that conduct water from the rock-salt mass, and especially by the sharp jump in the strength of the brine in well No. 3 upon its transition into the Salt-bearing stage. Thus, in the very lowest part of the Usolskoye Paleozoic we identify two water-bearing horizons: one developed above the deposit of clayey salt, with the water-bearing beds of the Bodarinian stage; the other enclosed within the very mass of the Salt-bearing stage. In the area of the Usolskoye deposit these horizons are evidently isolated; but they may probably approach and even be connected with one another through the upper part of the salt deposit, interbedded only with thin layers of clay.

All the water-bearing horizons listed are often connected in one way or another with the land surface, forming numerous springs and sources in the region. The emergence of underground waters associated with the first and second water-bearing horizons is in most cases determined by the intersection of the land surface with the water-bearing beds. It finds expression either in the form of ordinary springs of the type of descending sources, which are observed quite often on the left bank of the Angara River, or else in the form of the waterlogging of the meadow terrace, which is a common phenomenon in our region. Both are understandably observed especially often in synclines, where the Jurassic deposits descend toward the valley of the Angara River. But waters associated with the coal-bearing Jurassic may also emerge on the land surface under other conditions. For example, on the left slope of the Angara River, near the mouth of the Skipidarikha stream and the tannery works, a spring of artesian fresh water was noted above, emerging among a field of Jurassic rocks and evidently associated with tectonic disturbances in the middle part of the Spasskaya anticline. Among the Jurassic rocks such springs, however, occur comparatively rarely, which may be explained by their rapid weathering and by the development thereby of clayey products that clog the outlets of artesian water.

These disturbances, meanwhile, constitute the only conditions under which underground waters of deeper horizons may come out onto the land surface. They quite often determine the complex paths along which ascending water currents circulate, as indicated by the schemes of figs. 15 and 17. However, the geological conditions of our region by no means always make it possible directly

to observe the outlets of these waters directly, since the Paleozoic is often overlain by sandy-clayey products of the destruction of the Jurassic, or by recent river deposits, which conceal from the observer all the surface signs of deep groundwaters. Thus, the emergence onto the surface of pressure waters from deep horizons is possible here only in the absence of sandy-clayey river, recent or Jurassic deposits masking them, as is the case, for example, in Usolye in the upper part of Varnichnyi Island and in the resort park.

In connection with the resolution of a number of practical questions facing both the saltworks and the resort, it is expedient to touch also upon the conditions of the underground circulation of waters. In this respect the most important question is that of vertical circulation and, in connection with it, the origin of the ascending springs that bring salt water to the surface.

To explain the hydrostatic head that is evident here, it is sufficient to recall the basic elements of the tectonics of our area. It belongs to a rather strongly downwarped part of the southeastern limb of the Buret–Belsk anticline; moreover, the difference in the hypsometric position of the marly horizons of the Middle Cambrian in the crest of this anticline, below the village of Bureti, and in Usolye, for example at the pontoon, reaches approximately 150 m. This already creates conditions sufficient for the manifestation of a small head, at least in the upper aquifer horizon of the Cambrian. In addition, the Usolye area is also part of the other, northwestern Bulai anticline, being situated on the lowering of its northeastern limb, which must likewise favor ascending currents of water. But here it is especially necessary to bear in mind the position of the area in the general tectonic scheme of the Irkutsk Amphitheater, which includes the entire Irkutsk coal basin. All investigators of the Irkutsk basin and of the mountain systems adjoining it from the NE and SW suppose that, in the direction to the NE, toward the region of the Primorsky Mountains of Baikal, and to the SW, toward the northern foothills of the Eastern Sayan, increasingly deeper horizons of the Eo-Paleozoic are gradually brought to the surface; these, finally, in the opinion of some, are also gradually replaced by the underlying mass of the pre-Cambrian crystalline basement (10; 26; 31). Under these conditions, manifestations of hydrostatic head in our area are understandable.

Indeed, the nearest point to the town of Usolye where horizons of the Lower Cambrian, stratigraphically close to those of Usolye, come to the surface is the above-described Mount Bodara in the foothills of the Eastern Sayan. At the foot of this mountain there crops out a red-colored series of Moty sandstones, which we accepted above as the stratigraphic equivalent of the Usolye Saliferous Stage. If now the difference in absolute elevations between the level of the Angara River at the town of Usolye and the foot of Mount Bodara is taken as 70 m, then the difference in hypsometric position between the Usolye Saliferous Stage, lying in the town of Usolye at a depth of 700 m, and the series of Moty red-colored sandstones at the foot of Mount Bodara will amount to 770 m. It is by this magnitude that the hydrostatic head by which the salt brines in Usolye are brought to the surface is determined. But losses to friction, understandable under the conditions of the very complex subterranean paths along which the waters of the deep horizons circulate toward the town of Usolye, somewhat weaken this pressure, and the actual head observed in the deep boreholes is reduced to 700 m (boreholes No. 1 and No. 3).

The considerations just set forth clarify the general conditions of the head; but they do not explain certain particular phenomena in Usolye—for example, the differing height of the piezometric level in almost all boreholes and especially the phenomenon of gushing in the Almaznaya borehole, whose waters rise 12 m higher than in the nearest boreholes of Varnichnyi Island. In this small discrepancy in the magnitude of the head there are reflected the very complex lithological and tectonic conditions under which the deep...

lateral underground circulation of waters, and which, of course, may vary, in some cases increasing the aforementioned losses to friction, and in other cases leading to their diminution. In the latter respect, tectonic fissures and certain phenomena connected with them deserve special attention. It is known that every tectonic fissure, or even a crumpled zone of rocks, opens to the waters paths of least resistance, along which, for precisely this reason, underground waters always readily follow. Movement along these paths, consequently, must be accompanied by the smallest losses of head. Tectonic fissures may also lead to the same reduction of losses because in many cases they give a considerable shortening of the paths of circulation of underground water. This consideration is very important under the conditions of our district, where the Paleozoic mass of rocks, as was clarified at the beginning of the article, is gathered into numerous small, though gentle, folds, while the tectonic fissures cutting them persist for tens of kilometers. It is also necessary to point to the phenomenon of energetic leaching of limestones along fissures, with the formation of numerous small pores and even considerable cavities, the passage of which by underground waters must always likewise give a sharp reduction in losses to friction.

The observations made, we believe, are sufficient to explain the small differences in head that are observed in the Usolye district. The greatest head here will be given by those boreholes which cut through the largest number of significant tectonic fissures. The Almaznaya borehole, as was established in the preceding chapter, passed through a tectonically strongly shattered zone, and the flowing observed in it is a matter entirely comprehensible. Other deep boreholes in this respect are situated under less favorable conditions, as was also made clear above and shown in Fig. 17.

But in the regime of underground waters, besides hydrostatic head, the thickness of the aquifer also has great significance. In the town of Usolye all data are available for the underground waters to saturate, to a greater or lesser degree, that suite of limestones which overlies the Salt-bearing stage. It is closed by the overlying calcareous-clayey horizons of the Usolye stage and, being more or less permeable throughout its entire thickness, indicates a possible thickness of the pressure waters of up to 400 m. However, the waters of this limestone mass, according to the data of all boreholes, are distinguished by low salinity, which rises sharply at deep tectonic fissures (boreholes No. 1 and No. 3) and likewise suddenly gives a maximum strength in the Salt-bearing stage (Fig. 18; borehole No. 3). This compels one to consider it more probable that the saline waters are confined within the very mass of rock salt. Hence the aquifer connected with it must be regarded as the source of pressure waters of high salinity, understandable under conditions in which the salt deposit is washed; meanwhile, the waters above the next limestone mass come into contact with the clayey rock salt as with the bed of the aquifer—which, as is known, always gives only a small effect of leaching. In this case the pressure waters are expressed by a whole series of separate aquiferous beds of small thickness, in sum, however, amounting to more than 50 m.¹)

Thus, the underground waters of the deep horizons of the Usolye Paleozoic are under the conditions of an artesian basin, by which, in connection with the tectonic structure of the district, the vertical circulation of the waters is determined.

Closely connected with the phenomenon of vertical circulation of waters is their transfer from one aquiferous horizon to another, and hence the enrichment with salts of the fresh waters of the upper horizons, where, however, during subsequent bedded circulation, they are distributed unevenly. Naturally, the greatest enri—

¹) It is possible that in certain particular cases the enclosure of pressure waters may also be effected by tectonic fissures, with which, especially on their hanging wall, various tectonoclasts are associated, always accompanied by clayey products of grinding.

the enrichment with salts of each of the three upper horizons must be connected with sources of saline brines, i.e., with thrust fissures and zones of crushing of the rocks. From these same fissure lines, which in our area run along azimuths NW: 50°–60°, the saline waters are gradually diluted as a result of their mixing with fresh waters. Since here the greatest crushing of the rocks and the thrust fissures in the Usolye area are associated with the southeastern limbs of anticlinal folds, it should be expected that, from the axial line of each anticline broken by thrusts and crumpled, the saline waters will circulate through the aquiferous beds toward the southeast and will persist in that same direction over a more or less considerable distance, with a gradual weakening of the brine concentration; meanwhile, toward the northwest they will be quickly replaced by fresh waters. With the above-established dip of the entire Paleozoic sequence, moreover, toward the NE, similar bedded circulations of salt-enriched waters must also occur in a northeastern direction.

These considerations regarding the probable direction of bedded circulation of salt-enriched waters may have great practical significance, opening the possibility, by means of shallow drilling, of locating the zones of aquiferous horizons richest in brines. From this same point of view, the prospecting work already carried out in 1899 and 1915 on Spassky Island acquires great interest, especially for the Usolye resort; together with the probable scheme of the tectonic structure of the locality, it makes it possible to mark out salt-bearing areas on the island, as has been done on the tectonic map of Fig. 4.

In concluding the description of the underground waters it is necessary also to touch upon the question of their chemical composition. In Appendix V a number of the most characteristic analyses are given of brine from various boreholes and of samples of rock salt obtained by borehole No. 1 and No. 3. Here, therefore, we shall confine ourselves only to clarifying the general features of the chemical composition of the waters.

It must be said that, both in the published printed literature and in unpublished archival materials, a large number of analyses of the Usolye brines is known. But all these analyses suffer from one shortcoming: they give some idea of the composition and properties of the underground waters in the form in which they emerge onto the surface in natural springs and sources, i.e., in the form of mixed waters from all aquiferous horizons. Throughout the long history of the saltworks there was not a single attempt to sample and analyze the waters of different horizons, and it is understandable that decidedly all the analyses have as their heading only the name of a borehole, a bath, or a well. Hence arises the difficulty of making sense of these analyses, since the peculiarities of the composition of the waters of individual horizons are unknown. The operators of the saltworks and of the resort, however, have long been struck by one feature of the waters of the upper aquiferous horizons: the rather large amount of hydrogen sulfide emitted by them, which is strongly felt near the Brodovich borehole and especially at the flowing Almaznaya borehole in the resort park, where the influence of hydrogen sulfide is sharply reflected even in the surrounding, rapidly dying vegetation. Attention is drawn to this in his latest report to the All-Union Mining Scientific-Technical Congress in April 1926 by mining engineer A. I. Sosov (46), who indicates that the brines of boreholes No. 2, Brodovich, and Almaznaya differ sharply from the brine of borehole No. 3 by their high hydrogen-sulfide content. The analyses presented in Appendix V make it possible to add to this that the three named boreholes differ just as sharply from borehole No. 1 as well, in whose brine, at its concentration of 17° B., only 1.50 g of sulfuric anhydride per liter is contained, whereas the brine of the Brodovich borehole, at a concentration of only 9° B., yields 3.9 g of sulfuric anhydride. If one takes into account that boreholes No. 1 and No. 3, poor in hydrogen sulfide, receive brine from the lower aquiferous horizon, while the others

the wells are fed by waters chiefly of the upper Paleozoic horizon, where, as was shown above, the water-bearing rocks are the bituminous limestones of the Usolye stage, then the source of hydrogen sulfide in the wells will be obvious. Another peculiarity of these same waters consists in the comparatively low strength of the brines, which usually does not exceed 10° B., which, after all that has been said about the distribution and circulation of underground waters and about the sources of their salinity, requires no further comment.

As regards the composition of the waters of the very lowest water-bearing horizon, at present brought to the surface by well No. 1 and well No. 3, we can judge them for the time being, from the few known analyses, only from well No. 1. Here, first of all, it is necessary to note their high saturation with salts, reaching up to 20° B and higher, and at some moments even approaching the state of supersaturation. Further noteworthy is the great purity of the brine obtained, which, with 180.14 g of sodium chloride per liter, contains only 2.79 g of other salts. Characteristic, finally, is the complete absence, in all brine analyses known up to now, of potassium salts.

Of great interest are also the analyses of various samples of rock salt obtained from well No. 1, given in the same Appendix V. These analyses reveal the comparatively slight purity of the salt, containing, apparently even in the best samples, 9.31% of water-insoluble residues¹). But it is distinguished by the almost complete absence of other soluble salts, amounting to only 0.33%. Analyses of interbeds of clayey salt already give 2.75% calcium sulfate. The quantity of insoluble residue in these interbeds reaches 41.55%. Very interesting, too, is the note of the analyst of the Irkutsk gold-assaying laboratory, from whose document we borrow the analyses of rock salt from well No. 1 (50): “Potassium is found in all three samples.”

Recently analyses have been made of samples of rock salt also from well No. 3, the data of which are given in the same appendix (53). From here eight analyses were made of samples taken at different horizons, which gives an idea of the composition of the salt along the vertical section of the deposit. The data of these analyses repeat, in general, the features of the chemical composition noted above. It should nevertheless be pointed out that the interbeds of rock salt here reveal greater purity, since the quantity of insoluble residue in five samples falls to 2%–5%; magnesium gives only traces, while the quantity of sodium chloride in some samples reaches 91.50%, with a moisture content of 5%. Characteristic, finally, are the more definite indications of potassium. This element was established in the very uppermost horizons of the deposit and in only one of the eight samples. In this connection the analyst’s data contain the remark only of “traces” of potassium²).

Regime of the Waters of the Wells and Boreholes of the Usolye Deposit

The data presented in the preceding chapters on the geological structure of the Usolye district, as well as on the distribution and circulation of underground waters, make it possible to resolve a number of practical questions facing the deposit, and first of all questions connected with the regime of the wells and boreholes.

¹) It is very probable that the contamination of the salt in this case is due to the technical conditions of drilling with the Keystone apparatus—which is to a certain extent confirmed by the data, cited below, of the analysis of salt from well No. 3.

²) Worthy of attention is the fact that precisely in the upper layers of the deposit, where potassium was established, in the section of well No. 1 (Appendix III, layer No. 34) a reddish-gray coloration of the salt is indicated, passing downward into pink, with the total thickness of the layer being 4.88 m.

In the regime of the groundwater of the Usolye district, the main questions are those concerning the height and constancy of the head, the strength of the brine supplied by the wells, and the quantity of inflowing water, or the yield. In this connection, the following questions of a more particular character are always posed here and resolved in different ways: 1) A certain concordance between the regime of all the wells of the Salt-works Island and the level of the waters of the Angara River. 2) Concordance of the height of the head in Brodovich’s well and No. 2 and in the nearest wells. 3) The independence of the regime of the Almaznaya well and the phenomenon of flowing in it. 4) Different yield in the wells, greatest in Brodovich’s well and then in well No. 2. 5) The comparatively high strength of the brine in these two wells and, conversely, the low strength in the same horizons of wells No. 1 and No. 3. 6) A sharp jump in the strength of the brine, observed at great depth in wells No. 1 and No. 3.

Almost all the questions posed were directly or indirectly illuminated in the preceding chapters, and therefore here we shall dwell on them as briefly as possible.

As regards the first and second of these questions, they find their explanation in the lithological composition of the upper horizons of the Usolye deposit. In the stratigraphic outline of the deposit it was established that, both in the valley of the Angara River and on a considerable part of its islands, recent river deposits are widely distributed, and that these deposits in many places are underlain by the coal-bearing Jurassic, which in its upper horizons is most often represented also by loose formations. Such a composition of the underlying rocks of the valley makes quite probable a rather deep penetration of the waters of the Angara River and their inevitable influence upon the saline waters of the upper water-bearing horizons. Hence there is an equal possibility of such influence in all the adjacent wells and boreholes and a connection in their regime, irrespective of the original tectonic relations between them, especially under the conditions of the uncased wells of the Salt-works Island. This influence of the waters of the Angara River upon the wells and boreholes was established long ago by mining engineer A. I. Sosov (51). By it must also be explained the connection in the regime of the adjacent wells—Brodovich’s and No. 2, whose piezometric level is determined by the level of the water standing in the Angara River, and, when one of them is operated, always changes in the other, as also in the nearest wells, in view of the formation, understandable under the indicated conditions, of a cone of depression. Such influence of the Angara River is strengthened in the present case also by those same fault fissures and bands of disturbed rocks near which these wells were sunk. It should weaken in tectonically quiet areas, and also as the well is deepened.

The considerations just set forth make understandable also the independence from the Angara River of the regime of the Almaznaya well, situated on the elevation of the left slope of the valley, where there are no recent river deposits. As to the question of the mutual connection of the regime of the Almaznaya well, Brodovich’s, and No. 2, we have no factual material whatever. According to the tectonic scheme of Fig. 17 such a connection is entirely possible; but it can be established only by special methods of investigation. The same tectonic scheme of Fig. 17 also explains the phenomenon of flowing in the Almaznaya well—which was already clarified in the preceding chapter. Here one may nevertheless raise the question of the causes of the absence of such flowing in Brodovich’s well and No. 2, which are situated under conditions close to those of the Almaznaya. In this question, in our opinion, of very substantial importance is the position just mentioned of the latter well, which lies outside the influence of the waters of the Angara River; and along with this also the fact that it is the only one of all the wells cased to its full depth. And when Brodovich’s well or well No. 2 is cased throughout its full depth, when, consequently, the influence of the mighty Angara River that lowers the head will here be excluded, and along with it the same influence of the upper water-bearing horizons destroyed, then the head in these wells will undoubtedly rise. This head, after all,

will probably be less than that yielded by the Almaznaya borehole, since the tectonic fissures in both Brodovich’s borehole and borehole No. 2 are apparently connected with thick clayey horizons, which must inevitably weaken the head.

The scheme in Fig. 17 finally makes clear both the different discharge of the boreholes and the differing strength of the brine they supply. Brodovich’s borehole and No. 2, which at a shallow depth intersected a system of fissures of a major fault, must, understandably, yield both a higher discharge and a stronger brine than boreholes No. 1 and No. 3, which at the same depths passed through a tectonically calm zone¹.

Undoubtedly, the same intersection of a major tectonic fissure must also explain that abrupt jump in the strength of the brine from 6°–6.5° B. to 16°–18° B., recorded at great depth in boreholes No. 1 and No. 3 (Fig. 17).

The area of the upper part of Varnichny Island, like the left bank of the Angara River in the district of the three deep boreholes we have examined, is characterized in general by strong tectonic compression of the rocks, as shown on the map in Fig. 4; and, owing to the probable development here of an entire system of fault fissures, it is distinguished by fairly strong brines that either emerge directly at the surface as salt springs, or are connected with the very uppermost water horizons, as occurs in exploratory borehole No. 5 of 1915.

As for the regime of deep boreholes No. 1 and No. 3, situated in the lower and middle parts of Varnichny Island, it raises no particular questions. But in both boreholes the change in brine strength with depth, shown—together with other boreholes—on the diagram in Fig. 18, is of great interest. Both these boreholes, in the upper horizons, as has already been indicated, give a comparatively low brine strength, fluctuating within the limits of 1%–5%; whereas borehole No. 2, in the same horizons, gives brine up to 7%–9%, which was also observed in Brodovich’s borehole. This brine strength, with slight fluctuations in borehole No. 3 and rising slowly in borehole No. 1, reaches its maximum in both boreholes at a depth of about 200 m. In borehole No. 3 such a maximum was first observed at 180 m, where the brine reached a strength of almost 7.5%; after a noticeable decrease, at a depth of about 200 m, there was a second maximum with a strength up to 7.5%; below that the strength again decreased, reaching a third maximum of 8% strength at a depth of about 250 m. After this the brine quickly dropped to 4.5% strength and, decreasing further slowly to 4 and 3.5%, retained this value down to a depth of 425 meters. Within approximately the same strength range of 4–7%, the brine persisted down to the 593 m horizon, where it showed a sudden jump to 17%; and at a depth of 691 m, already within the mass of rock salt, from 19% strength it also suddenly reached 27% and 29.6%.

In borehole No. 1 the strength of the brine reaches as much as 4.5% at a depth of 210 m; lower down, after a slight decrease, it rises to 5.2% at a depth of about 240 m and then, having fallen to 4.5%, remains at this level down to the 640 m horizon. At the depth of the latter horizon the brine gives a sudden jump to 14% strength, and still lower rises almost to 18%.

Similar changes in strength with depth are also revealed by the diagram in Fig. 18 in the other boreholes. Here the first maximum of strength coincides with the above-mentioned upper Paleozoic aquifer. It is also characteristic that in borehole No. 1, below the named aquifer, from a depth of 235 m to 260 m, the bottom proved completely dry; deeper, evidently owing to slow inflow from the upper horizons, the standing water level rose again, and from a depth of about 450 m, with small fluctuations, remained at the very edge of the casing pipes (Fig. 18).

The fluctuations in brine strength in the Almaznaya borehole have a different significance. The first

a maximum of 5.5–7.5%, observed here at a depth of 150 to 210 m, coincides with a zone of tectonic disturbances; the second, of the same origin, was at a depth of 260 m; and, finally, the third, at 6%, at the bottom of the borehole, may be connected with the first Paleozoic aquifer occurring here, as a result of an overthrust or flexure, at a great depth. For borehole No. 3 one may also note an individual feature, namely that at a depth of 50 to 120 m there was observed in it a rather high strength of brine, 7.5%, which was not found here in borehole No. 1. This phenomenon may be connected with the intersection of fractures, quite possible under conditions of small folds of the second order of the Varnichny synclinal. A special position is occupied also by that sudden jump in the strength of the brine which was observed at a depth of 640 m in borehole No. 1 and at a depth of 593 m in borehole No. 3. Above, we connected it with a very probable large tectonic fissure here. A similar second jump at a depth of 691 m in borehole No. 3 indicates the isolated position of an aquifer horizon confined to the salt deposit.

As regards, finally, the exploratory boreholes on the area of Spassky Island, they all have a very small depth, not more than 40 m, and in most cases are characterized by waters of low salinity, which, however, are of great interest for the health resort. In the latter respect the greatest interest belongs, first of all, to borehole No. 2, drilled in 1915, situated near the steamboat landing stage and encountering at a depth of 12 m brine of a strength of 7.5° B. As is evident from the tectonic map, fig. 4, it is situated, like exploratory borehole No. 5 on Varnichny Island, on the south-eastern side of the strongly disturbed belt of the resort and of Brodovich’s borehole. At a short distance from this borehole, along the Aleksandrovsky road, is borehole No. 1, of the same year of exploration, which encountered brine of 8° B, but already at a depth of 17 m. The brine of both boreholes is undoubtedly connected with one and the same Jurassic aquifer horizon, and its deeper occurrence in borehole No. 1 confirms the sinking of the Paleozoic in a south-eastern direction. The occurrence at this point of saline water is quite natural with the bedding circulation of waters from the crumpled belt of Varnichny Island, according to the south-eastern dip of the rocks. To the southeast of the village of Ugolnik there is also a series of boreholes with saline waters. The presence of saline water in boreholes Nos. 2 and 5, 1899, and Nos. 3 and 4, 1915, situated on one belt of north-eastern direction, also indicates the probable proximity to them of a series of overthrust fissures. A fairly strong disturbance evidently also passes near boreholes No. 5 of 1899 and No. 3 of 1915, since, according to the sections of these boreholes, their saline waters are connected with one and the same Jurassic aquifer horizon, but in the latter they were encountered at a depth of 12 m, and in the former at a depth of 20 m. In connection with the probable disturbances here also stands the phenomenon of slight flowing of borehole No. 5, which is noted in the drilling log. Also noteworthy is the rather deep position of the saline-water horizon in borehole No. 4 of 1915, which confirms the gradual lowering of the Paleozoic, and with it the Jurassic with its aquifer horizons, toward the northeast.

In conclusion to the above review of the groundwaters and their regime it is of interest to add a few further considerations on the question of the possible yield of the boreholes.

As is known, the yield of each aquifer horizon is determined by the size of the underground water basin and of the catchment area feeding it, by the thickness of the aquiferous bed and by the rate of percolation of the water, and for artesian basins also by the magnitude of the head (38a; 46). Under the conditions of the Usolye deposit we are at present deprived of any possibility of determining exactly either the size of the basin or the rate of percolation of the water at the bottom of the borehole. We can only name the minimum thickness of the aquiferous bed that supplies the boreholes with strong brines, defining it as at least 50 m,

indicate a head of 700 m, and at the same time say that the volume of our basin must be very considerable, while the rate of seepage is comparatively small, since the water-bearing rocks are clayey rock salt and limestone. Under these conditions, determination of the yield is possible only by a purely empirical method in each already drilled borehole; attempts at this have already been made. However, taking into account the entire aggregate of the geological conditions of the deposit, we can outline that setting and even name within it those areas where the greatest yield may be expected. Given the probable considerable size of our water basin, the undoubted vastness of the catchment area, and the indicated thickness of the aquifer, generally speaking, the yield of the Usolye deep boreholes may be very large, and in each particular case must depend on the rate of seepage of water to the intake of the borehole. This rate will be lower in limestones and in rock salt that retain the normal strength of a fairly dense rock; but it will be greater in the same rocks where they are tectonically disrupted and destroyed, and greater still where the aquifer is cut by a tectonic fissure or, possibly, by an entire system of such fissures. In each of the cases named, accordingly, the yield will also increase; it should be especially considerable and reliable where tectonic fissures occur that are most developed along strike, and such, most probably, must be those encountered by boreholes at great depth.

Thus, it may be said that in the Usolye district the greatest yield should be expected in boreholes that encounter major tectonic disturbances at great depth. Significant disturbances may, to be sure, also occur at shallow depths, where they may likewise give a large borehole yield, an example of which we see in Brodovich’s borehole. But, apart from the possible occurrence of such a fissure at the same shallow depths, which would exclude its being fed by strong brines, these fissures, even with their direct connection with deep horizons, are less interesting because the strong brines circulating through them are subject to the inevitable freshening influence of the waters of the upper horizons. It is precisely this case, most likely, that we have both in Brodovich’s borehole and in No. 2.

From the indicated point of view, the greatest yield, while preserving the brine’s high strength, can be expected only in deep tectonic fissures. Such fissures in the region of the Usolye deposit, according to the scheme of its geological structure given in the preceding chapters, may be expected in every more or less significant and especially tectonically crumpled synclinal fold. At the same time, owing to the usual displacement of disturbances toward the SE, some indication of disturbances in the deep zones of a given syncline may be provided by second-order, broken anticlines observed at the surface and to the SE of it, as we have in the Varnichnaya syncline of the Usolye deposit. And the more significant and sharply expressed the syncline is, the greater the possibility of encountering deep tectonic fissures in it. In them we may expect both the greatest borehole yield and, at the same time, the least losses of head, as was clarified earlier. Within the narrow limits of the area of the Usolye deposit we described above two anticlines, the Izvestkovaya and Kurortnaya, and between them two synclines, the Varnichnaya and Yamanya. In the Varnichnaya syncline, deep boreholes No. 1 and No. 3 have already probably established a significant tectonic fissure. Similar fissures, and possibly even more significant ones, are also probable within the Yamanya syncline, which is expressed considerably more sharply than the former.*) Other zones of similar, but also important, significance may have—

*) Strictly speaking, the Kurortnaya anticline too should be assigned to the category of second-order anticlines, and its broken character serves as the surface expression of those disturbances that are developed at depth in the Varnichnaya syncline.

of surficial or near-surface disturbances—which occurs in the resort area and, probably, in the Spasskaya anticline. Given the full possibility of a high yield here, these zones are of great interest for the Usolsk resort, which exploits brines of low strength.

As for the absolute values of well discharge, the attempts made so far to determine them by bailing, unfortunately, have not once been carried through to completion, since the maximum productivity of bailing that developed in the process did not reach the critical point of the piezometric surface in the well. This fact alone indicates the probable high discharge of the wells. The most interesting experiments were carried out in 1926 by mining engineer A. S. Golovenkov, who conducted trial bailing of wells No. 1 and No. 3. During bailing, well No. 1 gave a lowering of the water level from a depth of 3 m to 16 m; the greatest discharge attained was about 10 cubic m, or up to 840 vedra per hour. The bailing that continued after this could no longer change the depth of the level, which remained constant. Almost the same results were obtained by trial bailing of well No. 1, where the discharge attained was 9.14 cubic m of water, with the water lowered to a constant level at a depth of only 12 m. It is evident that, in order to determine the true discharge here, powerful pumps must be used, which would make it possible to reach the critical point of the discharge curve¹.

Conclusion

The geological description of the deposit given above makes it possible to give the following brief characterization of its geological structure.

The Usolskoye rock-salt deposit in Irkutsk Governorate, which supplies the saltworks and the resort, belongs to the Irkutsk Cambrian, and, by the stratigraphic position of the salt body, probably pertains to the lower division of this system. The salt body is represented by a bed of complex composition, lying at a depth of about 700 m and, in the part of it opened by deep drilling, attaining a thickness of 70–75 m, with 57.3 m of useful salt thickness. The question of the true thickness of the salt-bearing series at Usolye is still unclear. It is, however, very probable that this thickness is considerably greater. The position of the Usolye district in the southern part of the Irkutsk Amphitheater, in the immediate vicinity of the Ancient Foreland of Asia, and the relation of the deposit, by age, to the beginning of the Cambrian period—that is, to a transitional moment in the life of the Sayan–Baikal geosyncline, when in its northern parts it was passing through an epoch of struggle between land and sea—give grounds for assuming here the possibility of the development of those basins which Shatsky (42) called monogeosynclines; and, in connection with them, according to De Launay’s theory (38; 31), the possibility of a series of salt deposits, as well as deposits of bitumens, of very great thickness.

In lithological composition of the salt-bearing series, in which interbeds of gypsum occur comparatively rarely, and from chemical analyses of the rock salt, which have revealed the presence of potassium in it, the Usolskoye deposit most probably belongs to the type of marine salts formed as a result of concentration in an isolated lagoon of the Cambrian sea (36, 300). But, since considerable quantities of potassium may also occur in continental deposits (41, 104–210), a more detailed study of the lithological composition of the salt-bearing stage is necessary in order to decide the question of the type of the Usolskoye deposit.

The rock-salt bed has as yet been studied very poorly, since it has been penetrated only partly, by just two boreholes (No. 1 and No. 3), and we cannot yet judge its horizontal extent. For the present we can only consider it probable that the salt-bearing sequence retains the above-indicated thickness of the bed over an area of not less than 1 sq. km., and therefore the probable reserve of rock salt may be taken at about 140 million tons. The possible reserves must be many times greater.

The great depth at which the bed occurs makes its direct exploitation by shafts difficult, and therefore the saltworks is, for the time being, limited to evaporating salt from strong brines supplied by deep boreholes. These brines are the result of the leaching of rock salt by the underground waters of an aquifer connected with the salt-bearing sequence; under the artesian-basin pressure conditions they rise upward. Since, moreover, through the action of the folding phenomena of the Jurassic and Cretaceous periods, the entire sequence of the Usolye Cambrian proved to be broken up by numerous, more often small, disturbances of the bedding-displacement type and sometimes by larger overthrusts, the saline brines, under the indicated pressure conditions, spread through the aquifers of the upper stages of the Cambrian and of the Ust-Baley suite, and under suitable conditions also come out at the surface in the form of salt springs and sources. The waters of these horizons are distinguished by a low salinity (5°–10° Baume), but, because of their very shallow depth of occurrence, they are exploited by the Usolye resort. In addition to their low strength, the waters of the upper horizons are rich in hydrogen sulfide, produced by the leaching of bituminous limestones of the upper stage of the Middle Cambrian.

As regards the question of possible directions for exploitation of the deposit in the near future, it may develop in different directions.

One may exploit brines of low strength obtained from natural springs or wells and shallow boreholes, as the saltworks did until recently and as the resort does to the present day. But one may also exploit the primary source of the salt waters, in the form of the rock-salt bed lying at great depth, either by direct mining with the aid of a shaft—which the managers of the Irkutsk mining industry have lately begun to consider seriously—or by obtaining natural strong brines from the depths of this bed. In each of the indicated cases, the deposit may be approached in different ways.

In the case of exploiting brines of low strength, both the saltworks, situated on Varnichny Island, and the Usolye resort, located opposite it, occupy a very advantageous position, since their territory is connected with a belt of fairly intense tectonic disturbances that conduct brines from deep horizons. From the resort park through Varnichny Island this belt passes onto Spassky Island (Fig. 4), in the lower part of which the same favorable conditions are preserved. Enrichment by brines of the upper aquifers continues for a comparatively short distance upstream along the Angara River (for the Jurassic about 0.5 km), which is fully preserved also on Spassky Island. In using these brines, the site on Spassky Island situated directly above the Varnichny belt of disturbances should be considered especially favorable, since the brines here are connected with the Jurassic aquifer lying at a depth of 10 to 20 m and can easily be used by shallow boreholes. But this site is not the only one in the deposit area in the indicated respect. In the upper half of Spassky Island, near the village of Ugolnik, there is a new belt of disturbances, the intensity and scale of which are not yet known; but the enrichment of the Jurassic aquifer by brines is beyond doubt here as well. With simple additional drilling in this area, more enriched horizons can easily be found. Closer to the left bank of the Angara River they should occur at a depth of 10–12 m, which to the northeast, toward the village of Zhilkina, should increase rather rapidly. A similar probable belt ...

tectonic disturbances and, at the same time, the enrichment with brines of the upper horizons of the rocks also occurs in the northern part of the deposit, below deep borehole No. 1. But this area, which includes the lower summit of Varnichnyi Island and the upper part of Berezovyi Island, is less favorable in the sense that Jurassic deposits are almost or entirely absent here, the aquiferous horizon of which serves as a collector for the saline waters flowing in from below. Hence the use of ascending brines by shallow boreholes is possible here only directly from tectonic fissures, the discovery of which under the indicated conditions may be no easy matter.

It should finally be noted also that the geological conditions of the Usolskoye deposit in Irkutsk Governorate are not rare, and in the vast areas of Cambrian development here one could point to a whole series of districts very favorable for the use of ascending brines. I shall indicate only one district, situated near the town of Usolye and possessing all the data for its possible development. This is the Malta district. Here there passes a whole series of zones of tectonic disturbances, which conduct saline water to the surface, causing the development of solonchaks and salt springs, which were mentioned in the geological sketch of the Cheremkhovo district. In recent years a climatic station has been established at Malta.

As for the second possible direction of exploitation of the Usolskoye deposit, here in turn there may be two methods: the exploitation of solid rock salt by means of a mine, and the exploitation of natural brine by means of deep boreholes. With regard to the first method it must first of all be noted that, in the geological description of the deposit, a number of facts were cited indicating a strong aquiferous horizon which is connected with the bed of rock salt, and which would create extremely difficult working conditions in this direction. For a final decision of this question, however, it is necessary to have a fuller idea of the thickness and composition of the bed, and the possibility is not excluded that in deeper horizons the bed will prove to be completely dry, as is the case in many deposits, and in particular in the Bakhmut district of the Donets Basin. (37; 7, 16).

The exploitation of strong brines by deep boreholes imposes other requirements on the Usolskoye deposit. In this respect, the method of operating deep boreholes now being applied at the salt works, called the compression method, deserves attention first of all (1). The method consists in forcing weak brine into a borehole under pressure up to 7 atmospheres—which, in the opinion of local practitioners, should cause artificial leaching of the rock-salt deposit and the emergence to the surface through the same borehole of brine of high concentration (the brine is poured into the annular space and comes out of the borehole through the pipe, or vice versa). Developing the same idea further, the local engineers propose to sink two deep boreholes side by side and to build all further exploitation on the principle of two communicating vessels: weak brine obtained from Brodovich’s borehole, or even fresh water, is forced under pressure into one borehole; through the other a strong brine gushes, issuing to the surface in quantities equal to that forced in.

In the theoretical justification of this method, and in all subsequent constructions, the deep borehole is regarded as a simple physical system of two communicating vessels. Indeed, all the boreholes of Usolye in all aquiferous horizons, especially in the Paleozoic, always reveal confined waters—which, in particular, in borehole No. 1, in the operation of which this method was first applied, is manifested in a water level close to the edge of the casing pipe, and which, when a pipe of small diameter is lowered into the borehole, gives two columns of water constituting the indicated physical system. However, under these conditions, to speak of creating the setting of communicating vessels and to think,

that the injected water, or weak brine, must wash over and leach the bed of rock salt, overcoming enormous pressure (about 80 atm.) and, upon reaching the day surface as “artificial” brine, would mean denying the existence under natural conditions of yet another, geological, aspect of the question, which greatly complicates the entire physical system and consists in the following.

The experience of operating borehole No. 1 by the so-called compression method is somewhat reminiscent of the original method of determining the yield of an artesian well by pouring water into it. So long as the quantity of water poured in is less than the discharge, it disappears in the well quite without trace, exerting no influence on the piezometric surface of the well, which is determined by the physical conditions of the artesian basin as a whole, usually embracing very extensive areas, measured in hundreds and even thousands of square kilometers. The water-bearing horizon associated with the salt-bearing sequence of Usolye likewise represents an enormous artesian basin, whose pressure waters receive their hydrostatic pressure from the foothills of the Eastern Sayan and the Baikal region; and the injection of water into this powerful basin cannot attain the effect on which the compression method relies.

However, this injection can, to a certain extent, achieve the result expected by the practitioners of the saltworks, but in only one case, namely: if the geological conditions characterizing the borehole being exploited are indeed close to the physical system of communicating vessels. The latter is possible when the brine at the bottom of the borehole is more or less isolated from the artesian basin as a whole, or, in other words, when the velocity of seepage of water at the bottom is so low that the connection of the borehole with the artesian basin is practically negligible. Thus, the implementation of the compression method of exploitation, to the extent to which it is planned by the saltworks, is possible only in those boreholes which, with a low seepage velocity, are distinguished by a low discharge.^1 There, however, where the connection of the borehole with the artesian basin is effected by tectonic fissures, and where the boreholes yield a fairly high discharge, this method will not achieve any appreciable results, apart from a certain dilution of the brine and its simple delivery, which can easily be carried out without the use of injection. The latter is fully applicable to boreholes No. 1 and No. 3, which at great depth have evidently intersected a large tectonic fissure and, according to the data of A. S. Golovenkov, must have a fairly high discharge.

Thus, here too we arrive at the same conclusion that was developed in the preceding chapter, namely: in the exploitation of strong brines, irrespective of the method employed, the greatest guarantee of successful operation in all respects can be provided by deep zones of tectonic disturbances, where we encounter both a high strength of the brine and the greatest discharge and, finally, the highest pressure. It follows from this that, in the further study of the Usolskoye deposit, the central place should be occupied by the study of its tectonics. Until such time as our knowledge of the tectonics is limited only to the uppermost zones of the Usolye formations, exploration must pay serious attention to large synclinal depressions. In exploitation, however, it will for the present be necessary to confine oneself to the limits of the Varnichnaya syncline, with the possible transfer of the plant’s operations also to the left bank of the Angara River, below the resort park.

^1 It must be said, however, that under these conditions the compression method has not yet been sufficiently tested, and it is quite possible that here it will not give the same results as in boreholes No. 1 and No. 3.

Appendix I.

SECTIONS FROM THE BOREHOLES OF THE 1899 EXPLORATION¹.

Borehole No. 1.

(In the yard of the saltworks office).

No.	Layer	Thickness, m
1.	Vegetative layer and black earth	1.16
2.	Yellow sand	0.05
3.	Yellow-gray sand, compacted	1.09
4.	Pebble gravel in yellow sand	0.96
5.	Coal with loam	1.78
6.	Gray clay	0.02
7.	Brown coal	0.20
8.	Gray clay	0.41
9.	Brown coal	0.78
10.	Gray clay, fairly dense	0.58
11.	Clay with siliceous concretions, gray, crystalline	0.41
12.	Same, but the water left	1.78
13.	Same, but water appeared	2.62
14.	Same	0.33
	Total	12.17

Borehole No. 2.

(On Spassky Island)

No.	Layer	Thickness, m
1.	Vegetative layer and black earth with a salty taste	0.33
2.	Yellow sandy clay	0.02
3.	Gray clay	1.32
4.	Yellow-gray sand	0.94
5.	Sand of a dark-yellow color	0.15
6.	Pebble gravel in sand of a dark-yellow color	0.13
7.	Same, but the sand is coarse, with fine quartz pebble gravel	1.55
8.	Rock, the same (pebble gravel in sand)	0.91
9.	Yellow sand, with fine pebble gravel	0.51
10.	Light-gray sand, with siliceous concretions, fairly dense	0.18
11.	Brown coal, black in color, dense, crumbles, burns well	1.67
12.	Coaly earth	0.74
13.	Brown coal	0.05
14.	Sandy clay, gray, dense	0.89
15.	Coaly earth of a brown color	1.65
16.	Light-gray sandy clay, very dense	0.58
17.	The same clay, but with inclusions of flint	0.01
18.	Same	0.71
	Total	12.34

Borehole No. 4.

(On Spassky Island).

No.	Layer	Thickness, m
1.	Soil	—
2.	Gray-yellow sand	0.10
3.	Pebble gravel in sand (river sand, quartz); the pebble gravel occurs as rounded grains	2.24
4.	Sand with pebble gravel	2.46
5.	Coarse light-gray sand, very dense	2.29
6.	Sandy clay of gray color	3.38

1. Sandy clay with siliceous concretions and signs of carbonaceous earth, thickness 2.29 m.
2. Brown clayey shale, dense, greasy to the touch, thickness 6.30 m.
3. The same, thickness 3.05 m.

Total: 22.11 m.

Borehole No. 5

(On Spassky Island).

No.	Description	Thickness
1.	Alluvial sand, light-yellow in color, fine	2.59 m
2.	The same	1.90 m
3.	Coarse sand, gruss-like	0.02 m
4.	Pebble gravel in sand (many boulders occur)	1.07 m
5.	Coarse sand, gruss-like	2.16 m
6.	Gray sandy clay, rather coarse	0.63 m
7.	Grayish-white sand, coarse, compacted	0.90 m
8.	Gray clay, sandy, fairly dense	0.69 m
9.	The same	2.18 m
10.	Brown clayey shale, dense	0.20 m
11.	Dark-gray clay, greasy	0.61 m
12.	Light-brown clay, greasy	1.59 m
13.	Dark-gray clayey shale, dense, greasy	0.69 m
14.	Gray clay	0.63 m
15.	The same, but somewhat yellower in color	3.38 m
16.	The same1	2.13 m
17.	The same2	0.61 m
18.	Gray sand, coarse	0.61 m

Total: 22.68 m.

Borehole No. 6

(On Spassky Island)

No.	Description	Thickness
1.	Yellow clay	0.46 m
2.	Compacted whitish-yellow sand	1.22 m
3.	Coarse sand, loose	2.39 m
4.	Pebble gravel in sand	1.27 m
5.	The same	1.73 m
6.	Yellow sand, coarse	0.23 m
7.	Gray sand, very dense	6.10 m
8.	Brown coal	0.13 m
9.	Gray sandy clay, dense, with siliceous concretions	3.20 m
10.	The same, but softer	7.69 m
11.	The same	—

Total: 24.42 m.

Borehole No. 7

(On Spassky Island).

No.	Description	Thickness
1.	Yellow sandy clay	2.46 m
2.	Gray clay	0.05 m
3.	Yellow-gray sand	0.43 m
4.	Pebble gravel in sand	0.91 m
5.	The same pebble gravel in sand	2.18 m
6.	Light-gray sand, compacted	5.99 m
7.	Carbonaceous earth	1.04 m
8.	Gray sandy clay, with siliceous concretions	4.57 m
9.	The same	—

Total: 17.63 m.

Appendix II.

SECTIONS BY THE EXPLORATION BOREHOLES OF 1915¹.

Borehole No. 1.

(On Spassky Island).

No.	Description	Thickness, m
1.	Soil	0.17
2.	Light-gray sand	4.39
3.	Light-gray pebble rock with sand	4.58
4.	Plastic blue clay	0.02
5.	Interlayer of hard coal	0.66
6.	Gray clayey shale	2.19
7.	Clayey sandstone, fine-grained, hard, alternating with coarse-grained reddish sandstone; the color in both cases light gray	2.45
8.	Gray sand	3.35
9.	Same, red-brown2	2.13
10.	Brown clayey shale; interlayer of coal	7.76
11.	Blue-colored clayey shale	2.13
12.	Same, with pyrite	0.91
13.	Clayey sandstone, fine-grained, with black inclusions, shaly, light gray, dense3	1.64
14.	Same4	4.26
15.	Clayey shale with pieces of pyrite, blue	0.64
16.	Same, with pieces of flint5	2.90
17.	Same, with inclusions of flint and pyrite, light, bluish-gray6	1.72
18.	Dark-gray sandstone, very dense	1.49
19.	Clayey shale with pyrite and limestone, gray-brown	—
	Total	43.39 m

Borehole No. 2.

(On Spassky Island)

No.	Description	Thickness, m
1.	Soil	0.70
2.	Red sandy clay	2.13
3.	Fine sand	5.69
4.	Brown clayey shale7	3.09
5.	Same, bluish-gray	0.87
6.	Fine-grained brown sandstone, dense, with inclusion of coal	—
7.	Gray clayey shale8	1.25
8.	Same9	1.00
9.	Dark quartzite, very hard	0.06
10.	Same10	—
	Total	14.79 m

Borehole No. 3

(On Spassky Island).

No.	Description	Thickness
1.	Soil	—
2.	Sand with fine pebble, yellow-brown	1.85 m
3.	Coarse pebble	0.38 m
4.	Same¹	1.38 m
5.	Clayey sandstone, coarse-grained, dark gray, with mica	2.21 m
6.	Sandstone, blue-gray, hard, with mica and dark inclusions²	2.26 m
7.	Same, but weak³	0.68 m
8.	Clayey shale, brown⁴	2.90 m
9.	Same, with sulfur pyrite	3.71 m
10.	Same⁵	2.28 m
11.	Clayey sandstone, gray-brown, weak, fine-grained⁶	1.85 m
12.	Clayey shale, dark gray, with inclusions of quartz⁷	0.93 m
13.	Fine sand, brown-gray, with quartz⁸	0.14 m
14.	Clayey shale, green-gray, dense⁹	0.61 m
15.	Coarse sand, dark gray, with pieces of quartz	0.12 m
16.	Same, but finer and darker¹⁰	0.34 m
17.	Clayey sandstone, dark gray, fine-grained	0.25 m
18.	Same, but coarse-grained¹¹	0.12 m
19.	Clay with flint, dark gray¹²	—
20.	Same¹³	—

Total . . . 22.01 m

Note: Strength of the brine according to Baumé: 1) 0.9° 2) 2.35° 3) 2.8° 4) 2.95° 5) 2.92° 6) 2.92° 7) 2.95° 8) 2.95° 9) 2.9° 10) 2.92° 11) 2.92° 12) 2.93° 13) 2.92°.

Borehole No. 4

(On Spassky Island).

No.	Description	Thickness
1.	Soils	0.64 m
2.	Gray sand	5.76 m
3.	Pebble with sand	2.77 m
4.	Clayey shale, light gray	1.81 m
5.	Sandy clay, brownish-gray, with coal	1.04 m
6.	Sandstone, bluish-gray, weak, coarse-grained, with mica	2.90 m
7.	Brown coal with gray weak sandstone¹	0.38 m
8.	Sandstone, fine-grained, yellowish-gray, weak	0.59 m
9.	Fine sand, yellowish-gray	0.08 m
10.	Sandstone, coarse-grained, bluish-gray, weak, with mica	4.43 m
11.	Same, but clayey and darker²	0.68 m
12.	Clayey shale, dark brown, lighter with depth³	4.48 m
13.	Clayey shale, light gray, farther down passes almost into white⁴	7.80 m
14.	Clayey sandstone, bluish-gray, weak, with mica and sulfur pyrite⁵	2.15 m
15.	Clayey shale with inclusions of quartz, light gray⁶	2.79 m
16.	Sandstone with sulfur pyrite, light gray, weak⁷	0.87 m
17.	Clayey shale with sulfur pyrite, bluish-white⁸	0.70 m
18.	Clayey sandstone, grayish-brown, weak⁹	2.83 m
19.	Grayish-brown sand¹⁰	—
20.	Quartzite, decomposed, dark gray¹¹	—

Total . . . 42.70 m

Note: Strength of the brine according to Baumé: 1) 0.5° 2) 0.7° 3) 1.2° 4) 2.0° 5) 1.9° 6) 2.6° 7) 2.9° 8) 3.0° 9) 3.0° 10) 3.2° 11) 3.1°.

Borehole No. 5

(On Varnichny Island).

No.	Description	Thickness
1.	Dark-gray sand with pebble	1.06 m
2.	The same	4.43 m
3.	Gray clay¹	1.67 m
4.	The same, but with flint	1.81 m
5.	Brownish-gray sandstone, coarse-grained, with pyrite, weak²	1.34 m
6.	The same	0.34 m
7.	Brown clayey shale	1.34 m
8.	Gray sandstone, with quartz and pyrite, hard³	0.34 m
9.	The same⁴	—
	Total	12.33 m

Note: Strength of the brine according to Baumé: 1) 9.3° 2) 7.7° 3) 7.6° 4) 7.6°.

Appendix III.

SECTIONS OF DEEP BOREHOLES¹.

Brodovich Borehole.

(On Varnichny Island).

No.	Description	Thickness
1.	Sand	3.81 m
2.	Pebble	2.82 m
3.	Limestone	14.52 m
4.	Limestone with cracks and cavities filled with clay	41.80 m
5.	Dark-gray chert with pyrite	11.80 m
6.	Light-gray calcareous friable rock with inclusions of gypsum	31.86 m
7.	Limestone	41.20 m
8.	Clay	8.79 m
9.	Clayey shale	9.70 m
10.	Clay	8.53 m
11.	Clayey calcareous shale	15.58 m
12.	Fragments of red sandstone	—
	Total	190.41 m

Borehole at Malta Station.

No.	Description	Thickness
1.	Gray sand with coarse pebble	3.66 m
2.	Gray clay with inclusions of siliceous concretions and an admixture of pyrite	4.88 m
3.	Siliceous dolomite with inclusions of chert and pyrite	6.71 m
4.	Siliceous limestone of dark-gray color	10.97 m
5.	Dolomitized siliceous limestone, with inclusions of pyrite	12.19 m
6.	Calcareous-clayey shale	2.44 m
7.	Dolomitized limestone	18.29 m
8.	Limestone	3.05 m
9.	Siliceous dolomite	3.05 m
10.	Dolomitized limestone with inclusion of pyrite	6.10 m
11.	White crystalline limestone	8.89 m

¹ In view of the need, as far as possible, to reduce the volume of the present article, the sections of deep boreholes given below are presented with a generalization of a number of beds according to the ready-made graphic diagrams kept in the archive of Solzavod, and only in the most critical parts of the sections are exact copies from the drilling journals given. The numerical material of the originals in all appendices has been left unchanged.

No.	Rock	Thickness, m
12	Dolomitized limestone	3.05
13	Light-gray dolomite	8.89
14	Dolomitized limestone	2.74
15	White porous limestone	10.06
16	Dolomitized limestone	7.93
17	Dark-gray dolomite with inclusion of sulfur pyrite	27.71
18	Dark-gray limestone	6.71
19	Black bituminous dolomite	41.46
20	Dark-brown shaly calcareous clay	32.92
21	Dolomitized limestone	9.75
22	Limestone	15.24
23	White tuff-like limestone with a coating of gypsum	18.29
24	Dark-blue calcareous clay	9.64
25	Gypsum	1.05
26	Limestone with interbeds of gypsum	4.25
27	Limestone	3.96
28	Dark-blue clayey shale	20.67
29	Limestone with interbeds of gypsum	4.20
30	Hard limestone	3.05
31	Same	10.06
32	Hard clayey shale	2.74
33	Limestone	25.00
33	Clayey shale	16.15
35	Limestone	8.53
36	Clayey shale	7.01
37	Limestone	40.54
38	Limestone with interbeds of clayey shale	17.68
39	Limestone	4.85
40	Clayey shale	5.18
41	Limestone	21.03
	Total	470.63

Borehole No. 1.

(On Varnichny Island).

No.	Rock	Thickness, m
1	Vegetal layer and loam	3.35
2	River pebble gravel	7.32
3	Sand with pebbles	1.52
4	Gray clay, with sand	1.22
5	Dark-gray sand, soft	0.61
6	Light-gray clayey shale	3.05
7	Dark-brown clay	0.61
8	Bituminous limestone	76.81
9	Blue calcareous clay	8.84
10	Clayey limestone	122.3
11	Limestone	7.6
12	Clay	4.6
13	Gray limestone	26.0
14	Brownish-black limestone, variegated, of various composition	3.1
15	Light-gray clay	3.0
16	Limestone of light-gray to black color	15.9
17	Black clayey shale	1.5
18	Light-gray limestone	7.0
19	Limestone of various dark shades	5.4
20	Dark-brown limestone, dense	5.3
21	Brown limestone, with pieces of black clayey shale	5.2
22	Gray clay	1.5
23	Dark-brown limestone, with pieces of black clayey shale	4.0
24	Dark-brown limestone	6.1
25	Black limestone	10.9
26	Limestone with inclusion of flint and with interbeds of clayey shale	26.0
27	Dark-gray hard limestone	110.5
28	Limestone with interbeds of shale	1.83
29	Limestone	148.13
30	Limestone with gypsum and clayey shale	1.52
31	Limestone	66.52

No.	Description	Thickness, m
32.	Rock salt of grayish-white color	3.05
33.	Marl, dark gray, almost black, resinous	0.31
34.	Rock salt of reddish-gray color, gradually passing into pink, with small particles of shaly clay	4.88
35.	Rock salt, light gray, with brownish bituminous mud	9.45
36.	Resinous dolomite	0.91
37.	Resinous rock salt, with thin interbeds of dolomite	0.41
38.	The same, with interbeds up to 0.15 meter thick of bluish plastic clay with flint	1.12
39.	The same, with interbeds of dark clay	2.44
40.	The same, with interbeds of gray clay	2.59
41.	The same, with interbeds of dolomite and gypsum	0.61
42.	Fine-grained rock salt with interbeds of resinous dolomite	0.91
43.	Coarse-grained salt	0.61
44.	Fine-grained rock salt with interbeds of light-colored dolomite	0.91
45.	Fine-grained rock salt with interbeds of dolomite and clay	0.91
46.	Coarse-grained rock salt, dark-brown in the sample, colorless and transparent in individual fragments	2.44
47.	Rock salt with interbeds of gray, hard, shaly clay	3.36
	Total	722.04 m

Borehole No. 2.

(On Varnichny Island).

No.	Description	Thickness, m
1.	Calcareous clay	4.57
2.	Limestone with inclusions of crystals of gray pyrite	29.57
3.	Limestone without pyrite	90.83
4.	Limestone with interbeds of clayey shale	4.57
5.	Limestone	7.62
6.	Limestone with interbeds of clayey shales	5.49
7.	Limestone	19.51
8.	Red-brown calcareous sandstone	3.05
9.	Calcareous-clayey shale	3.05
10.	Red-brown calcareous sandstone	3.96
11.	Calcareous-clayey shale	6.10
12.	Red-brown calcareous sandstone	3.05
13.	Gray calcareous clayey shale	3.0
14.	Dark-gray calcareous clayey shale	13.8
15.	Light-gray clayey shale	1.5
16.	Limestone	21.3
17.	Brown calcareous clayey shale	17.3
18.	Gray calcareous clay	8.6
19.	Clayey limestone	1.5
20.	Gray calcareous clay	3.0
21.	Clayey limestone	6.1
22.	Gray calcareous clay	1.5
23.	Clayey limestone	3.0
24.	Calcareous clay	1.5
25.	Clayey limestone	12.2
26.	Gray calcareous clay	4.6
27.	Clayey limestone	1.5
28.	Gray calcareous clay	1.5
29.	Clayey limestone	1.5
30.	Clayey shale, calcareous	19.9
31.	Limestone	64.40
32.	Limestone with interbeds of clayey shale	50.90
33.	Limestone	3.96
34.	Limestone with interbeds of clayey shale	2.13
35.	Limestone with interbeds of clayey shale	21.34
36.	Limestone with interbeds of gypsum	4.57
37.	Limestone	25.30
	Total	477.95 m

Borehole No. 3

(On Varnichny Island).

No.	Description	Thickness, m
1	Yellow sand	7.01
2	River pebble gravel	2.13
3	Gray clayey limestone	10.67
4	Limestone with interbeds of clayey shale and inclusion of gray flint	1.52
5	Clayey limestone	9.75
6	Limestone	202.08
7	Limestone with interbeds of clayey shale	3.05
8	Clay	1.52
9	Limestone with interbeds of clayey shale	6.10
10	Clay	1.52
11	Limestone	35.06
12	Limestone with interbeds of clayey shale	1.52
13	Limestone	10.67
14	Limestone with interbeds of clayey shale and small grains of gypsum	1.52
15	Limestone	1.52
16	Limestone with interbeds of clayey shale	1.52
17	Limestone	110.06
18	Limestone with interbeds of clay	3.05
19	Limestone	8.84
20	Dark-gray limestone	0.5
21	Limestone	1.7
22	Dark-gray limestone	1.8
23	Limestone	1.0
24	Dark-gray limestone	12.3
25	The same, hard	18.9
26	Gray-colored limestone	5.4
27	Clayey shale	5.1
28	Gray limestone	0.4
29	The same, but hard	4.8
30	The same, of medium hardness	1.9
31	The same, hard	3.0
32	Hard limestone	4.3
33	Gray-colored limestone	3.3
34	Gray-colored limestone, and among it stone with gypsum, limestone, and small fragments of other rocks	42.3
35	Limestone	66.4
36	Limestone with interbeds of gypsum	1.5
37	Limestone	1.1
38	Gray-colored limestone	4.7
39	Limestone	65.4
40	Gray-colored limestone	8.4
41	Limestone	1.7
42	Gray-colored limestone	5.9
43	Limestone with small grains of salt	8.6
44	Gray-colored salt with interbeds of clay	0.5
45	Salt	1.0
46	Hard salt	33.1
47	Hard salt	1.3
48	Soft white salt	0.9
49	Hard salt	2.3
50	Soft salt, with a large quantity of clay	1.4
51	Soft salt, purer	1.0
52	Soft salt, pure, white	1.1
53	Hard salt	6.7
54	Soft, clayey salt	0.5
55	Marl	1.3
56	Quartz-mica sandstone	0.6
57	Gray salt	0.3
58	Gray, clayey salt	0.5
59	Clayey shale with siliceous concretions	4.85
60	Clayey shale with rock salt	0.7
61	Clayey rock salt	0.5
62	Strongly clayey salt	0.7

1. Argillaceous shale . . . . . . . . . . . . . . . . thickness 1.3 m
2. Argillaceous shale with thin interbeds of rock salt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . thickness 0.9 m
3. Argillaceous shale . . . . . . . . . . . . . . . . . thickness 2.0 m
4. Gray rock salt . . . . . . . . . . . . . . . . . . . thickness 2.0 m
5. The same, with hard argillaceous shale . . . . . . . . thickness 3.1 m
6. Rock salt and siliceous concretions in argillaceous shale . . . thickness 0.4 m
7. Argillaceous shale with thin interbeds of rock salt . . . . . thickness 0.9 m
8. Argillaceous shale . . . . . . . . . . . . . . . . . thickness 0.9 m

Total . . . 761.6 m

Appendix IV.

SECTIONS OF EXPLORATORY BOREHOLES, 1925

Borehole No. 1.

(On Varnichny Island).

1. Sand . . . . . . . . . . . . . . . . thickness 2.10 m
2. Silty clay with pebble . . . . . . . . . thickness 0.70 m
3. Dark-brown clay with pebble (quicksand) . . thickness 0.60 m

Total . . . 3.40 m

Borehole No. 2.

(On Varnichny Island).

1. Silty sand . . . . . . . . . . . . . . thickness 2.10 m
2. The same, with pebble . . . . . . . . . thickness 0.60 m
3. The same, pebble coarser (quicksand) . . . thickness 2.20 m
4. Gray sand . . . . . . . . . . . . . . thickness 0.70 m
5. The same, with pebble . . . . . . . . . thickness 0.90 m
6. Grusy sand with a dark-yellow tint . . . . thickness 1.10 m
7. Gray clay with a bluish tint . . . . . . . thickness 3.80 m
8. The same, with siliceous limestone . . . . . thickness —

Total . . . 11.40 m

Borehole No. 3¹).

1. Silty sand . . . . . . . . . . . . . . thickness 1.67 m
2. Limestone . . . . . . . . . . . . . . thickness —

Borehole No. 4.

1. Sand . . . . . . . . . . . . . . . . thickness 0.71 m
2. Gray clay with a bluish tint . . . . . . thickness 0.69 m
3. The same, with siliceous limestone . . . . thickness 0.30 m

Total . . . 1.70 m

Borehole No. 5.

1. Silty sand . . . . . . . . . . . . . . thickness 0.53 m
2. Gray clay with a bluish tint . . . . . . thickness 0.75 m
3. The same, with siliceous limestone . . . . thickness 1.17 m

Total . . . 2.45 m

¹) All the following boreholes were laid out on the left bank of the Angara River, below the resort park.

Borehole No. 6

No.	Description	Thickness
1.	Silty sand with pebble	1.28 m
2.	Sand with unrounded pebble	0.53 m
3.	Limestone	—
	Total	1.81 m

Borehole No. 7

No.	Description	Thickness
1.	Silty sand with pebble	1.92 m
2.	Sand with siliceous unrounded pebble	0.64 m
3.	Limestone (large, unrounded boulder)	—
	Total	2.56 m

Borehole No. 8

No.	Description	Thickness
1.	Silty sand	2.98 m
2.	Sand with pebble	1.07 m
3.	Gray clay with a bluish tint	0.42 m
4.	The same, with siliceous limestone	1.71 m
5.	Coarse pebble of siliceous limestone	—
	Total	6.18 m

Borehole No. 9

No.	Description	Thickness
1.	Vegetal layer	0.31 m
2.	Silty sand	2.02 m
3.	Sand with pebble (fine pebble)	0.75 m
4.	The same	—
	Total	3.08 m

Borehole No. 10

No.	Description	Thickness
1.	Silty sand	2.13 m
2.	Clayey sand with pebble (quicksand)	1.27 m
3.	Sand with pebble	3.40 m
	Total	6.80 m

Borehole No. 11

No.	Description	Thickness
1.	Silty sand	1.07 m
2.	Sand with pebble	3.83 m
3.	Gray clay with a bluish tint	0.43 m
4.	Siliceous limestone of milky-white color	—
	Total	5.33 m

Borehole No. 12

No.	Description	Thickness
1.	Silty sand	2.10 m
2.	Sand with pebble	2.90 m
3.	Limestone	0.32 m
	Total	5.32 m

Borehole No. 13

No.	Description	Thickness
1.	Vegetal layer	0.38 m
2.	Silty sand	0.19 m
3.	Sand with pebble	2.66 m
4.	Gray clay with a bluish tint, with siliceous limestone	—
	Total	3.23 m

Appendix V.

CHEMICAL ANALYSES OF BRINES¹

1. Analysis of the brine from the borehole at the village of Malta.

Component	Basis	Amount
Dry residue at 120°C	per 1 liter of brine	12.541 gr.
Chlorine	per 1 liter of brine	5.987 gr.
Sulfuric acid	per 1 liter of brine	1.616 gr.
Calcium oxide	per 1 liter of brine	0.881 gr.
Magnesium oxide	per 1 liter of brine	0.306 gr.
Oxides of iron and aluminum	per 1 liter of brine	traces
Sodium	—	3.751 gr.
Sodium oxide	—	—
Loss on ignition	—	—
Total		12.541 gr.

2. Analysis of the brine from the “Brodovich” borehole.

Component	Basis	Amount
Dry residue at 120°C	per 1 liter of brine	88.5 gr.
Chlorine	per 1 liter of brine	46.9 gr.
Sulfuric acid	per 1 liter of brine	3.9 gr.
Sodium oxide	per 1 liter of brine	2.2 gr.
Magnesium oxide	per 1 liter of brine	0.3 gr.
Oxides of iron and alum.	per 1 liter of brine	—
Sodium	per 1 liter of brine	30.4 gr.
Loss on ignition	per 1 liter of brine	—
Sodium oxide	per 1 liter of brine	0.2 gr.

3. Analysis of brine from the well at the resort baths.

Component	Amount
Dry residue	71.725 gr.
Chlorine	39.770 gr.
Sulfuric acid	3.534 gr.
Carbonic acid, combined	0.079 gr.
Carbonic acid, semi-combined	0.079 gr.
Carbonic acid, free	0.202 gr.
Silica	0.028 gr.
Sodium	25.608 gr.
Calcium oxide	1.868 gr.
Magnesium oxide	0.644 gr.
Oxides of iron and aluminum	0.009 gr.

Combination of salts.

Salt	Amount
Sodium chloride	65.138 gr.
Calcium sulfate	4.536 gr.
Magnesium sulfate	1.299 gr.
Magnesium chloride	0.501 gr.
Excess oxygen	0.054 gr.

4. Analysis of brine from the Diamond borehole in the resort park.

Component	Amount
Dry residue	45.048 gr.
Chlorine	23.571 gr.
Sulfuric acid	3.538 gr.
Carbonic acid, combined	0.141 gr.
Carbonic acid, semi-combined	0.141 gr.
Carbonic acid, free	0.166 gr.
Silicic acid	0.024 gr.
Sodium	15.143 gr.
Calcium oxide	1.899 gr.
Magnesium oxide	0.654 gr.
Oxides of iron and aluminum	0.080 gr.

Combination of salts.

Component	Amount
Sodium chloride	38.516 gr.
Calcium sulfate	4.415 ”
Magnesium sulfate	0.239 ”
Magnesium chloride	0.570 ”
Excess oxygen	0.096 ”

5. Borehole No. 1.

Brine of strength 17° Baumé (per 1 liter).

Elementary composition.

Component	Amount
Chlorine	109.42 gr.
Sulfuric anhydride	1.50 ”
Calcium oxide	1.17 ”
Magnesium oxide	0.01 ”
Iron oxide	0.05 ”
Sodium	70.92 ”
Total	183.07 gr.

Combination of salts.

Component	Amount
Calcium sulfate	2.54 gr.
Calcium chloride	0.23 ”
Magnesium chloride	0.02 ”
Sodium chloride	180.14 ”
Total	182.93 gr.

6. Elementary composition of a sample of drilling material from borehole No. 1 (in %).

Sample No. 1

Rock salt.

Component	Amount
Sodium chloride	88.4 %
Calcium sulfate	0.33 ”
Water-insoluble residue	9.31 ”

The water-insoluble residue showed the following:

Component	Amount
Calcium carbonate	25.95 ”
Calcium sulfate	2.55 ”
Aluminum oxide	5.51 ”
Iron oxide	20.7 ”
Silica	14.71 ”

Sample No. 2.

Layer of clayey salt.

Component	Amount
Sodium chloride	51.88 %
Calcium sulfate	2.75 ”
Water-insoluble residue	41.55 ”

The water-insoluble residue showed the following:

Component	Amount
Calcium carbonate	35.15 %
Calcium sulfate	12.25 ”
Aluminum oxide	5.43 ”
Iron oxide	6.67 ”
Silica	9.35 ”

Sample No. 3.

Layer of salt-bearing bituminous rocks.

Component	Amount
Sodium chloride	64.17 %
Calcium sulfate	2.02 ”
Water-insoluble residue	30.88 ”

The water-insoluble residue showed the following:

Component	Amount
Calcium carbonate	24.20 %
Calcium sulfate	4.40 ”
Aluminum oxide	9.30 ”
Iron oxide	12.20 ”
Silica	21.32 ”

Potassium is present in all three samples. Bromine and iodine were not detected.

7. Analyses of rock salt from borehole No. 3 (in %%).

Depth at which sample was taken, in meters	696,5	701,0	713,0	722,4 / 729,3	728,5	734,5	736,5	742,1
Type of salt sample	Strongly clayey	—	With clay	—	Dirty	Dirty-yellow	Dirty-yellow	—
Elementary composition.
Moisture at 110°C	6,344	5,592	9,002	7,768	9,420	4,960	7,132	5,200
Residue insoluble in water	15,184	3,932	15,272	4,568	9,972	1,796	3,480	5,000
Sulfuric anhydride	5,089	1,753	1,688	0,625	1,251	0,790	1,564	2,395
Chlorine	43,221	53,349	44,432	52,613	47,807	55,840	52,891	52,382
Calcium	2,560	1,071	0,786	0,600	0,937	0,537	0,751	1,271
Magnesium	—	Traces	Traces	—	—	Traces	—	—
Sodium	27,602	34,303	28,802	33,826	30,613	36,077	34,222	33,759
Potassium	Traces	—	—	—	—	—	—	—

On the basis of these data, the following combinations of salts were calculated:

Combination I.

Component	696,5	701,0	713,0	722,4 / 729,3	728,5	734,5	736,5	742,1
Moisture at 110°C	6,344	5,592	9,020	7,768	9,420	4,960	7,192	5,200
Residue insoluble in water	15,184	3,932	15,272	4,568	9,972	1,796	3,480	5,000
Calcium sulfate	7,208	2,483	2,391	0,885	1,772	1,119	2,215	3,392
Calcium chloride	1,223	0,946	0,330	0,943	1,154	0,577	0,333	0,760
Sodium chloride	70,011	87,047	73,087	83,836	77,682	91,548	86,840	85,648

Combination II.

(Without moisture and insoluble residue.)

Component	696,5	701,0	713,0	722,4 / 729,3	728,5	734,5	736,5	742,1
Calcium sulfate	9,185	2,744	3,158	1,012	2,198	1,200	2,478	3,777
Calcium chloride	1,558	1,045	0,303	1,076	1,430	0,619	0,374	0,846
Sodium chloride	89,257	96,211	96,539	97,912	96,372	98,181	97,148	95,377

Combination III.

(Washed salt.)

Component	696,5	701,0	713,0	722,4 / 729,3	728,5	734,5	736,5	742,1
Calcium sulfate	1,883	1,113	1,084	0,698	0,598	0,583	0,582	0,586
Sodium chloride	98,117	98,887	98,916	99,302	99,402	99,417	99,418	99,414

List of Literature Cited

A. PUBLISHED.

1. V. V. Kovrigin. A new phase in the salt industry of Siberia and the Far East.—Mining Journal, 1925, No. 2.
2. Description of the Irkutsk Saltworks and of its operation, established from 1823.—Mining Journal, 1828, IV.
3. On the operation of the Siberian saltworks in 1840.—Mining Journal, 1842, II.
4. F. Lvov. Report on work at the Irkutsk Saltworks.—Mining Journal, 1862, II.
5. Stempnevsky, mining engineer. Salt industries of Eastern Siberia.—Mining Journal, 1889, II.
6. A. Chekanovsky. Geological investigations in Irkutsk Governorate.—1874.
7. I. D. Chersky. Natural-historical notes and observations along the route from Irkutsk to N. Tunguska.—Proceedings of the East-Siberian Department of the Russian Geographical Society, vol. XV, Nos. 1–3.
8. I. D. Chersky. Geological investigation of the Siberian postal road. 1888.
9. V. A. Obruchev. Ancient Paleozoic sedimentary rocks of the valley of the Lena River, between the Kachug and Vitim stations.—Irkutsk, 1892.
10. K. I. Bogdanovich. Materials on the geology and mineral resources of Irkutsk Governorate.—Geological investigations and reconnaissance works along the line of the Siberian Railway, 1896, issue II.
11. A. Keppeh. Asia, the projected railways in it and its coal resources.—Mining Journal, 1835, No. 9.
12. Report of the Siberian Department of the Russian Geographical Society for 1868.
13. V. A. Obruchev. Deposits of brown coal in Irkutsk Governorate.—Mining Journal, 1891, vol. IV.
14. A. Ryabonsnitsky. On traces of a break in the Cambrian–Silurian deposits of the village of Padun on the Angara River and on the nature of their occurrence.—Notes of the St. Petersburg Mineralogical Society, part 48, 1912.
15. A. Ryabonsnitsky. Geological investigations in the upper reaches of the Kirenga River.—Materials on the Geology of Russia, 1918, 26.
16. G. Frederiks. Brief report on geological investigations in Irkutsk Governorate.—Proceedings of the Geological Committee, 1915, No. 9.
17. S. F. Malyavkin. On the Vilyui salt deposits.—Proceedings of the Geological Committee, 1911, vol. 30; minutes, pp. 184–6.
18. M. M. Tetyaev. The area of the village of Goremyki.—Transactions of the Geological Committee, 1916, New Series, issue 126.
19. M. K. Korovin. The Cheremkhovo coal district.—Proceedings of the Siberian Department of the Geological Committee, 1922, vol. II, issue 4.
20. M. K. Korovin. Geological investigations in Irkutsk Governorate in 1923.—Proceedings of the Geological Committee, 1925, vol. 43, No. 6.
21. M. M. Tetyaev. The basin of the Irkut and Kitoy rivers.—Proceedings of the Geological Committee, 1925, vol. 43, No. 6.
22. M. A. Usov. Tectonics of the Anzhero coal deposit.—Proceedings of the Siberian Department of the Geological Committee, 1920, vol. 1, issue 4.
23. K. I. Bogdanovich. On drilling for salt near Mal’ta station of the Siberian Railway.—Proceedings of the Geological Committee, 1913, vol. 32; minutes, pp. 344–346.
24. K. I. Bogdanovich. Ore deposits. 1904, vol. II.
25. D. I. Mushketov. Contemporary tectonic views in connection with the geology of Central Asia.—Proceedings of the Geological Committee, 1926, vol. 45, issue 1.
26. V. A. Obruchev. A brief outline of the tectonics of Siberia.—Bulletin of the Moscow Society of Naturalists, 1923–4.
27. M. A. Usov. Composition and tectonics of the deposits of the southern district of the Kuznetsk coal basin.—Novonikolaevsk, 1924.
28. D. Bakhund. On mylonites and tectonites.—Notes of the Russian Mineralogical Society, 2nd series, part 52, 1925.
29. M. A. Usov. Geology of caustobioliths.—Tomsk, 1920.
30. A. E. Fersman, academician. Geochemistry of Russia.—Leningrad, 1922.
31. M. M. Tetyaev. On certain fundamental questions of the geology of Siberia.—Bulletin of the Moscow Society of Naturalists, 1923–24.
32. Yu. A. Zhemchuzhnikov. Section of Jurassic coal-bearing deposits along the Angara.—Proceedings of the Geological Committee, vol. 44, No. 6.—1926.
33. M. A. Usov. Report on the activity of the Siberian Department of the Geological Committee for 1924.—Proceedings of the Siberian Department of the Geological Committee, vol. IV, issue 6, 1925.
34. M. A. Usov. Report on the activity of the Siberian Department of the Geological Committee for 1925.—Proceedings of the Siberian Department of the Geological Committee, vol. V, issue 6, 1926.
35. V. A. Azletsky. The Usolye resort and its therapeutic significance.—Irkutsk, 1924.
    35-a. M. G. Kurlov. Excursion to the therapeutic localities of Eastern Siberia.—Proceedings of Tomsk University, 1918.

1. Levinson-Lessing, F. Yu. Petrography—1925.

2. N. Yakovlev. Materials for the geology of the Donets Basin. (Rock salt, dolomites, and copper ores). Proceedings of the Geological Committee, N. S. vol. 94—1914.

3. K. I. Bogdanovich. Deposits of petroleum and other bitumens.—1920.

38-a. P. N. Chirvinsky. Textbook of Hydrogeology.—1922.

1. Natural productive forces of Russia. Vol. IV, issue 35. Salt.

2. Obrutschew, W. A. Geologie von Sibirien.—Berlin. 1926.

3. Grabau. Geology of the non-metallic mineral deposits other than silicates. Vol. 1. Principles of salt deposition.—1920.

4. Schuchert, Ch. Sitesman nature of the North American geosynclines.—Bull. Geol. Soc. Americ. V. 34, No. 2. 1923.

B. UNPUBLISHED.

1. From the “Chronicle of the Spassky Church of the village of Usolskoye, Irkutsk Eparchy” for 1704.—Materials of the East Siberian Branch of the Geological Committee.

2. Historical information on the Irkutsk Saltworks from 1765.—From materials of the East Siberian Branch of the Geological Committee.

3. Note of mining engineer A. I. Sosov. From materials of the East Siberian Branch of the Geological Committee.—File 545. 64–1.

4. A. I. Sosov. The Irkutsk Saltworks.—Report to the All-Russian Mining Scientific-Technical Congress in 1926.—From materials of the East Siberian Branch of the Geological Committee.

5. Plan of the environs of the Irkutsk Saltworks, showing the location of boreholes and brine wells.—From archival materials of the Irkutsk Saltworks.

6. V. A. Obruchev. Memorandum to the Mining Department in 1901.—From materials of the East Siberian Branch of the Geological Committee.—File 545-64–1.

7. A. S. Golovenkov. Memorandum on the condition of drilling operations at borehole No. 3 of the Irkutsk Saltworks.—From materials of the Western Siberian Branch of the Geological Committee.

8. Results of analyses of salt samples from borehole No. 3 in 1924. No. 1558.—From materials of the East Siberian Branch of the Geological Committee.

9. A. I. Sosov. On the brine economy of the works.—From the archive of the Irkutsk Saltworks.—File according to inventory No. 1, “On the operation of the works in 1915.”

10. A. V. Lvov, Prof. Explanatory note to the report of the commission on the question of further deepening one of the boreholes of the Irkutsk Saltworks.—From materials of the East Siberian Branch of the Geological Committee.—File 545-64-1.

11. Analyses of rock salt from borehole No. 3 of the Usolskoye Saltworks.—From materials of the East Siberian Branch of the Geological Committee.—File 545-64-1.

Description of Figures.

Fig. 1. Geological map of the Cheremkhovo district at a scale of 5 versts to 1 inch.

“ 2. Geological map of the district of the town of Usolye at a scale of 2 versts to 1 inch.

“ 3. Plan of Varnichny Island at a scale of 50 sazhen to 1 inch.

“ 4. Tectonic map of the Usolskoye deposit at a scale of 100 sazhen to 1 inch.

“ 5. Schematic longitudinal section along the right slope of the Angara River between the village of Barkhatova and the Ulyakha River.

“ 6. Schematic longitudinal section along the Bolshaya Belaya River from the village of Kholmushina to the village of Ust-Chernaya.

“ 6-a. Scheme of folds of the Bolshaya Belaya River.

“ 7. Normal section of the Paleozoic along the right slope of the Angara River in the sector: the village of Ponomareva—the village of Olonki.

“ 8. Malta zone of disturbances.

“ 9. Schematic longitudinal section along the left bank of the Angara River from the village of Telma to the village of Nechaeva.

“ 10. Transverse section across the valley of the Angara River.

“ 11. Section along the left bank of the Angara River from the pontoon bridge to Izvestkovy Cape.

“ 12 and 13. Sections of Varnichny Island.

“ 14. Fault in the park of the Usolskoye resort.

“ 15. Scheme of the tectonic structure of the Usolskoye deposit.

“ 16. Scheme of tectonics in the southern part of the Irkutsk Amphitheater.

“ 17. Sections of deep boreholes of the Usolskoye district, with a possible reconstruction of the main disturbance of the deposit.

“ 18. Diagrams of changes in brine strength and water level in the deep boreholes of Usolye.

Fig. 1

GEOLOGICAL MAP

of the southeastern margin

of the central district

of the Irkutsk Coal Basin

Scale: 1 : 210,000.

For the article by Prof. M. K. Korovin.

Legend

• Carboniferous deposits
• Lower and Middle horizons
• Upper horizon
• Paleozoic crystalline rocks
• Rock salt and salt springs
• Coal and traces of coal
• Outcrop line of coal-bearing strata

To the article
by Prof. M. K. Korovin.

Fig. 2.

GEOLOGICAL MAP

of the area of the Usolskoye deposit

Scale: 2 versts to an inch.

[Map]

Legend:

• Paleogene
• Jurassic
• Known boundary of the outcrop of variegated rocks
• Presumed boundary of the outcrop of variegated rocks
• Deep boreholes
• Saltworks

Fig. 3.

PLAN

of the Irkutsk Salt-Works

to the article by Mining Engineer M. K. Borovin:

THE USOLSKOYE DEPOSIT.

Scale: 100 sazhens to the inch.

(from the old survey)

N

Well No. 1

Karkur River

Well No. 3

Angara R.

boiling-house island

Well No. 2

Old channel

Ferry

Well Brodovaya

Well Almavnaya

S

Legend:

4. } Brine wells.

5. Exploratory borehole of 1912.

a. Boiling houses.
g. Graduation house.
s. Salt barns.
e. s. Electric station.
⊙ Deep wells.
| Outlets of salt springs.

Fig. 4.

Tectonic Map of the Usolskoye Deposit

To accompany the article by Prof. M. K. Korovin.

The petrographic base of the map is from the survey by engineer Kolchinsky in 1925.

Scale: 100 sazhen to the inch.

0 — 100 — 200 — 300 sazhen

Visible map labels:

• Berezovy Island
• Protoka
• Dolgorosky Island [[unclear: island name]]
• Salt
• [[unclear: large map label, partially cut off]]
• [[unclear: several small settlement/feature labels in the lower-right portion of the map]]

City of Usolye

Saltworks

Resort

Angara River

Island of the Angara River

Channel of the Angara River

Yamanyi Channel

Ferry

Angarsk Road

Barracks

Office

Shop

Hospital

Chapel

Stasskii

Semyorovo

Wells / boreholes indicated on the map: No. 1, 1925; No. 3, 1899; No. 4, 1901; No. 13, 1889; No. 14, 1901; No. 15, 1926; No. 16; No. 17; No. 18; No. 19; No. 20; No. 21; No. 22; No. 23; No. 24; No. 25; No. 26; No. 27; No. 28; No. 29; No. 30; No. 31; No. 32; No. 33; No. 34; No. 35; No. 36; No. 37; No. 38; No. 39; No. 40; No. 41; No. 42; No. 43; No. 44; No. 45; No. 46; No. 47; No. 48; No. 49; No. 50; No. 51; No. 52; No. 53; No. 54; No. 55; No. 56; No. 57; No. 58; No. 59; No. 60; No. 61; No. 62; No. 63; No. 64; No. 65; No. 66; No. 67; No. 68; No. 69; No. 70; No. 71; No. 72; No. 73; No. 74; No. 75; No. 76; No. 77; No. 78; No. 79; No. 80; No. 81; No. 82; No. 83; No. 84; No. 85; No. 86; No. 87; No. 88; No. 89; No. 90; No. 91; No. 92; No. 93; No. 94; No. 95; No. 96; No. 97; No. 98; No. 99; No. 100; No. 101; No. 102; No. 103; No. 104; No. 105; No. 106; No. 107; No. 108; No. 109; No. 110; No. 111; No. 112; No. 113; No. 114; No. 115; No. 116; No. 117; No. 118; No. 119; No. 120; No. 121; No. 122; No. 123; No. 124; No. 125; No. 126; No. 127; No. 128; No. 129; No. 130; No. 131; No. 132; No. 133; No. 134; No. 135; No. 136; No. 137; No. 138; No. 139; No. 140; No. 141; No. 142; No. 143; No. 144; No. 145; No. 146; No. 147; No. 148; No. 149; No. 150; No. 151; No. 152; No. 153; No. 154; No. 155; No. 156; No. 157; No. 158; No. 159; No. 160; No. 161; No. 162; No. 163; No. 164; No. 165; No. 166; No. 167; No. 168; No. 169; No. 170; No. 171; No. 172; No. 173; No. 174; No. 175; No. 176; No. 177; No. 178; No. 179; No. 180; No. 181; No. 182; No. 183; No. 184; No. 185; No. 186; No. 187; No. 188; No. 189; No. 190; No. 191; No. 192; No. 193; No. 194; No. 195; No. 196; No. 197; No. 198; No. 199; No. 200; No. 201; No. 202; No. 203; No. 204; No. 205; No. 206; No. 207; No. 208; No. 209; No. 210; No. 211; No. 212; No. 213; No. 214; No. 215; No. 216; No. 217; No. 218; No. 219; No. 220; No. 221; No. 222; No. 223; No. 224; No. 225; No. 226; No. 227; No. 228; No. 229; No. 230; No. 231; No. 232; No. 233; No. 234; No. 235; No. 236; No. 237; No. 238; No. 239; No. 240; No. 241; No. 242; No. 243; No. 244; No. 245; No. 246; No. 247; No. 248; No. 249; No. 250; No. 251; No. 252; No. 253; No. 254; No. 255; No. 256; No. 257; No. 258; No. 259; No. 260; No. 261; No. 262; No. 263; No. 264; No. 265; No. 266; No. 267; No. 268; No. 269; No. 270; No. 271; No. 272; No. 273; No. 274; No. 275; No. 276; No. 277; No. 278; No. 279; No. 280; No. 281; No. 282; No. 283; No. 284; No. 285; No. 286; No. 287; No. 288; No. 289; No. 290; No. 291; No. 292; No. 293; No. 294; No. 295; No. 296; No. 297; No. 298; No. 299; No. 300; No. 301; No. 302; No. 303; No. 304; No. 305; No. 306; No. 307; No. 308; No. 309; No. 310; No. 311; No. 312; No. 313; No. 314; No. 315; No. 316; No. 317; No. 318; No. 319; No. 320; No. 321; No. 322; No. 323; No. 324; No. 325; No. 326; No. 327; No. 328; No. 329; No. 330; No. 331; No. 332; No. 333; No. 334; No. 335; No. 336; No. 337; No. 338; No. 339; No. 340; No. 341; No. 342; No. 343; No. 344; No. 345; No. 346; No. 347; No. 348; No. 349; No. 350; No. 351; No. 352; No. 353; No. 354; No. 355; No. 356; No. 357; No. 358; No. 359; No. 360; No. 361; No. 362; No. 363; No. 364; No. 365; No. 366; No. 367; No. 368; No. 369; No. 370; No. 371; No. 372; No. 373; No. 374; No. 375; No. 376; No. 377; No. 378; No. 379; No. 380; No. 381; No. 382; No. 383; No. 384; No. 385; No. 386; No. 387; No. 388; No. 389; No. 390; No. 391; No. 392; No. 393; No. 394; No. 395; No. 396; No. 397; No. 398; No. 399; No. 400; No. 401; No. 402; No. 403; No. 404; No. 405; No. 406; No. 407; No. 408; No. 409; No. 410; No. 411; No. 412; No. 413; No. 414; No. 415; No. 416; No. 417; No. 418; No. 419; No. 420; No. 421; No. 422; No. 423; No. 424; No. 425; No. 426; No. 427; No. 428; No. 429; No. 430; No. 431; No. 432; No. 433; No. 434; No. 435; No. 436; No. 437; No. 438; No. 439; No. 440; No. 441; No. 442; No. 443; No. 444; No. 445; No. 446; No. 447; No. 448; No. 449; No. 450; No. 451; No. 452; No. 453; No. 454; No. 455; No. 456; No. 457; No. 458; No. 459; No. 460; No. 461; No. 462; No. 463; No. 464; No. 465; No. 466; No. 467; No. 468; No. 469; No. 470; No. 471; No. 472; No. 473; No. 474; No. 475; No. 476; No. 477; No. 478; No. 479; No. 480; No. 481; No. 482; No. 483; No. 484; No. 485; No. 486; No. 487; No. 488; No. 489; No. 490; No. 491; No. 492; No. 493; No. 494; No. 495; No. 496; No. 497; No. 498; No. 499; No. 500; No. 501; No. 502; No. 503; No. 504; No. 505; No. 506; No. 507; No. 508; No. 509; No. 510; No. 511; No. 512; No. 513; No. 514; No. 515; No. 516; No. 517; No. 518; No. 519; No. 520; No. 521; No. 522; No. 523; No. 524; No. 525; No. 526; No. 527; No. 528; No. 529; No. 530; No. 531; No. 532; No. 533; No. 534; No. 535; No. 536; No. 537; No. 538; No. 539; No. 540; No. 541; No. 542; No. 543; No. 544; No. 545; No. 546; No. 547; No. 548; No. 549; No. 550; No. 551; No. 552; No. 553; No. 554; No. 555; No. 556; No. 557; No. 558; No. 559; No. 560; No. 561; No. 562; No. 563; No. 564; No. 565; No. 566; No. 567; No. 568; No. 569; No. 570; No. 571; No. 572; No. 573; No. 574; No. 575; No. 576; No. 577; No. 578; No. 579; No. 580; No. 581; No. 582; No. 583; No. 584; No. 585; No. 586; No. 587; No. 588; No. 589; No. 590; No. 591; No. 592; No. 593; No. 594; No. 595; No. 596; No. 597; No. 598; No. 599; No. 600; No. 601; No. 602; No. 603; No. 604; No. 605; No. 606; No. 607; No. 608; No. 609; No. 610; No. 611; No. 612; No. 613; No. 614; No. 615; No. 616; No. 617; No. 618; No. 619; No. 620; No. 621; No. 622; No. 623; No. 624; No. 625; No. 626; No. 627; No. 628; No. 629; No. 630; No. 631; No. 632; No. 633; No. 634; No. 635; No. 636; No. 637; No. 638; No. 639; No. 640; No. 641; No. 642; No. 643; No. 644; No. 645; No. 646; No. 647; No. 648; No. 649; No. 650; No. 651; No. 652; No. 653; No. 654; No. 655; No. 656; No. 657; No. 658; No. 659; No. 660; No. 661; No. 662; No. 663; No. 664; No. 665; No. 666; No. 667; No. 668; No. 669; No. 670; No. 671; No. 672; No. 673; No. 674; No. 675; No. 676; No. 677; No. 678; No. 679; No. 680; No. 681; No. 682; No. 683; No. 684; No. 685; No. 686; No. 687; No. 688; No. 689; No. 690; No. 691; No. 692; No. 693; No. 694; No. 695; No. 696; No. 697; No. 698; No. 699; No. 700; No. 701; No. 702; No. 703; No. 704; No. 705; No. 706; No. 707; No. 708; No. 709; No. 710; No. 711; No. 712; No. 713; No. 714; No. 715; No. 716; No. 717; No. 718; No. 719; No. 720; No. 721; No. 722; No. 723; No. 724; No. 725; No. 726; No. 727; No. 728; No. 729; No. 730; No. 731; No. 732; No. 733; No. 734; No. 735; No. 736; No. 737; No. 738; No. 739; No. 740; No. 741; No. 742; No. 743; No. 744; No. 745; No. 746; No. 747; No. 748; No. 749; No. 750; No. 751; No. 752; No. 753; No. 754; No. 755; No. 756; No. 757; No. 758; No. 759; No. 760; No. 761; No. 762; No. 763; No. 764; No. 765; No. 766; No. 767; No. 768; No. 769; No. 770; No. 771; No. 772; No. 773; No. 774; No. 775; No. 776; No. 777; No. 778; No. 779; No. 780; No. 781; No. 782; No. 783; No. 784; No. 785; No. 786; No. 787; No. 788; No. 789; No. 790; No. 791; No. 792; No. 793; No. 794; No. 795; No. 796; No. 797; No. 798; No. 799; No. 800; No. 801; No. 802; No. 803; No. 804; No. 805; No. 806; No. 807; No. 808; No. 809; No. 810; No. 811; No. 812; No. 813; No. 814; No. 815; No. 816; No. 817; No. 818; No. 819; No. 820; No. 821; No. 822; No. 823; No. 824; No. 825; No. 826; No. 827; No. 828; No. 829; No. 830; No. 831; No. 832; No. 833; No. 834; No. 835; No. 836; No. 837; No. 838; No. 839; No. 840; No. 841; No. 842; No. 843; No. 844; No. 845; No. 846; No. 847; No. 848; No. 849; No. 850; No. 851; No. 852; No. 853; No. 854; No. 855; No. 856; No. 857; No. 858; No. 859; No. 860; No. 861; No. 862; No. 863; No. 864; No. 865; No. 866; No. 867; No. 868; No. 869; No. 870; No. 871; No. 872; No. 873; No. 874; No. 875; No. 876; No. 877; No. 878; No. 879; No. 880; No. 881; No. 882; No. 883; No. 884; No. 885; No. 886; No. 887; No. 888; No. 889; No. 890; No. 891; No. 892; No. 893; No. 894; No. 895; No. 896; No. 897; No. 898; No. 899; No. 900; No. 901; No. 902; No. 903; No. 904; No. 905; No. 906; No. 907; No. 908; No. 909; No. 910; No. 911; No. 912; No. 913; No. 914; No. 915; No. 916; No. 917; No. 918; No. 919; No. 920; No. 921; No. 922; No. 923; No. 924; No. 925; No. 926; No. 927; No. 928; No. 929; No. 930; No. 931; No. 932; No. 933; No. 934; No. 935; No. 936; No. 937; No. 938; No. 939; No. 940; No. 941; No. 942; No. 943; No. 944; No. 945; No. 946; No. 947; No. 948; No. 949; No. 950; No. 951; No. 952; No. 953; No. 954; No. 955; No. 956; No. 957; No. 958; No. 959; No. 960; No. 961; No. 962; No. 963; No. 964; No. 965; No. 966; No. 967; No. 968; No. 969; No. 970; No. 971; No. 972; No. 973; No. 974; No. 975; No. 976; No. 977; No. 978; No. 979; No. 980; No. 981; No. 982; No. 983; No. 984; No. 985; No. 986; No. 987; No. 988; No. 989; No. 990; No. 991; No. 992; No. 993; No. 994; No. 995; No. 996; No. 997; No. 998; No. 999; No. 1000.

LEGEND

— Branch of the railway.

— Country roads.

— Fence.

— Exploratory works of 1925: boreholes and wells.

— Deep boreholes.

— Exploratory boreholes of previous years. \[summer?] — Anticlinal zones. — Synclinal zones. — Crumpled folds of the second order. — Areas established by exposures. — Areas inferred. \} tectonic disturbances and stratification, washed by brines. \(\dfrac{C}{B}\) Depth of occurrence of brine in meters; strength of the brine according to Baumé. ## Visible map labels Molotov St. Match Factory. Factory Lane. Ostrov Tselma \[?] Protoka \[Channel] Ostrov Ugol’skii. Tel’ma. Os. \[Ostrov\] [unclear]

Borehole No. 2, 1899.

Borehole No. 1, 1899.

Borehole No. 6, 1899.

Borehole No. 5, 1899.

Borehole No. 3, 1915.

Cartographic Establishment under the Tomsk Colonization-and-Resettlement Party, Island No. 8.

Fig. 5. Schematic longitudinal section along the right slope of the Angara River between the village of Barakhatova and the village of Ulyanka.

Labels visible in the figure:

• v. Barakhatova
• K. Buret
• B. Buret
• Bagulina
• Kulakova
• Polovareva
• Solena
• stream Ulyan
• Level of the Angara River

Fig. 6. Schematic longitudinal section along the Bolshaya Belaya River from the village of Khomutina to the village of Ust-Chernaya.

Labels visible in the figure:

• v. Khomutina
• Level of the B. Belaya River
• v. Ust-Buret
• [[unclear: small route-plan inset with letters “S” and “SE”]]

Legend

• Cambrian non-salt-bearing deposits
• Limestone outcrops
• Recent deposits
• Lower boundary of the Cambrian
• Salt springs from fracture waters

Fig. 7. Normal section of the drift deposits along the right slope of the Angara River on the stretch: v. Pozdnyakova—s. Olonki.

Labels visible in the figure:

• Pozdnyakovskaya Factory
• II. Kamennaya
• D. Kruta Polyakova
• Pozharevskaya Hollow
• G. Semenkina
• N. Khud, meadow terrace
• s. Olonki
• Level of the Angara River

Scale:
horizontal: 1 cm—600 m;
vertical: 1 cm—60 m.

Fig. 8. Mal'ta zone of disturbances.
Scale: horizontal: 1 cm = 50 m; vertical: 1 cm = 10 m.

A. Outcrops of rocks within the zone of disturbances.

Visible annotations:
Pr. NO 350°–40°; Pr. SO ∠13°; Pr. NO 600; Pr. SO ∠25°; Pr. NO 400; Pr. SO ∠40°.

B. Possible reconstruction of the disturbances.

Legend

• Limestones of the upper occurrence.
• Breccia-like conglomerate.
• Fault-like striated limestone.
• Limestone, broken and crumpled.
• Cavities.
• Tectonic line.

Fig. 9. Schematic longitudinal section along the left bank of the Angara from the village of Tel’ma to the village of Nechaeva.
Scale: horizontal: 1 cm = 500 m; vertical: 1 cm = 66 m.

Visible labels along the section:

• Level of the Angara River
• village of Tel’ma
• Tel’ma bog
• Kommunal’nyi Plant
• Sityach. Factory
• Police post on the Angara River
• Resort (Salt Works)
• Izvestnyi Cape
• Angara River
• village of Zaitseva
• village of Nechaeva

Legend

• Paleozoic limestone.
• Fault lines.
• Jurassic deposits.
• Upper thin-layered Tertiary band.

To the article by Prof. M. M. Kornilov: “The Usolskoye Deposit…”

Fig. 10. Cross-section through the valley of the Angara River along the line: Deep Barakhlovskaya borehole—borehole No. 4, 1915—borehole No. 3, 1915—borehole No. 5, 1915—borehole No. 6, 1899—borehole No. 7, 1899—borehole No. 2, 1899—left bank of the Angara River.

Scale:
horizontal: 1 dm—1000 m;
vertical: 1 dm—100 m.

Labels visible in the figure: SW; NE; level; Angara River; Barakhlovskaya borehole; borehole No. 4, 1915; borehole No. 3, 1915; borehole No. 5, 1915; borehole No. 6, 1899; borehole No. 7, 1899; borehole No. 2, 1899.

Fig. 12. Section of Varnichnyi Island along the line: Brodovich borehole—borehole No. 3—borehole No. 1.

Scale:
horizontal: 1 cm—50 m;
vertical: 1 cm—5 m.

Labels visible in the figure: level; Angara River; Brodovich borehole; borehole No. 2; borehole No. 3; borehole No. 1.

Fig. 13. Section of Varnichnyi Island along the line: borehole No. 5 (1915)—brine well No. 3—borehole No. 2 (1925)—deep borehole No. 1.

Scale:
horizontal: 1 cm—50 m;
vertical: 1 cm—5 m.

Labels visible in the figure: level; Angara River; borehole No. 5, 1915; brine well No. 3; borehole No. 2 (1925); deep borehole No. 1.

Fig. 11. Section along the left bank of the Angara River from the [[unclear: bridge name]] bridge to Izvestkovy Cape.
Scale: horizontal, 1 cm = 50 m; vertical, 1 cm = 5 m.

Visible labels: North Brodyaga; borehole No. 2; Gazebo; Kamennistaya; Stolbovaya; Izvestkovy Cape; Angara River; Paleozoic; Yuri; boreholes; spring.

Fig. 11-a.
Scale: horizontal and vertical, 1 cm = 50 m.

Visible labels: Angara River; level 40; Paleozoic; Angara River.

Fig. 14. Ejection in the park of the Usolye resort.

Legend

• Paleozoic limestones.
• Outcrops of Paleozoic limestones.
• Jurassic deposits.
• Breccia-like clay conglomerate.
• Recent deposits of the Angara River.
• Small exploratory boreholes and pits.
• Deep borehole; brine well.
• Boreholes exploited for lithium exploration.
• Established boundary of the Paleozoic.
• Probable boundary of the Paleozoic.
• Fault lines.

Visible orientation labels: N; S.

Fig. 15.
Scale: 1 cm = 40 vertical.

Visible labels: North Brodyaga; Adamov [[unclear: spring or well]]; borehole No. 2; resort ejection; S; Yu.

Conventional symbols

• Zones of disturbance.
• Tectonics.
• Cambrian.
• Crystalline plate of the Precambrian.

Fig. 16.

Visible labels: SE; NW.

Fig. 17. Sections of deep boreholes in the Usolye district, with a possible reconstruction of the main fault of the deposit. Scale 1:5000.

To the article by Prof. M. K. Korovin: “The Usolye Deposit…”

Visible labels on the figure:

• Vertical scale: meters, from +100 to 800 m.
• Level.
• Mother well.
• SE.
• Angara well.
• Sal. Brodyaga.
• Well No. 2.
• Well No. 3.
• Well No. 1.
• NW.
• R. Angara.
• Brine 6.5°B.
• 16°B.
• Brine 6°B.
• 18°B.
• \(I_1\), \(I_2\)
• I, II, III
• A, B

Legend

• Clays and clayey shales.
• Sands, sandstones, and conglomerates.
• Limestones and clayey limestones.
• Bituminous limestones.
• Tectonoclasts.
• Rock salt.
• Gypsum interbeds.
• Fault fissure.
• I, II, III — stages.
• \(I_1, I_2\) — horizons.
• A, B — two variants of the fault.

Fig. 18. Diagrams of changes in the strength and thickness of salt in deep boreholes of the Usolye Irkutsk Province.

Diagram of changes in the strength of salt in borehole No. 3.

Scale of salt strength in %.
Meters.

Diagram of changes in the strength of salt in borehole No. 2.

Scale of salt strength in %.
Meters.

Diagram of changes in the strength and thickness of the salt in borehole No. 1.

Scale of salt strength in %.
Depth of salt in borehole.
Meters.

Visible stratigraphic and explanatory labels:

• Strong salt.
• Roof mudstone.
• First occurrence of salt.
• Strong salt.
• Stratification of beds.
• Outcrop of the lower salt.
• Clayey thickness.
• Boundary of standing level of brine.
• Standing brine level in the borehole — 33.1 m.

Diagram of salt strength in a gallery of the resort.

Scale of salt strength.
Analytical.
Meters.

1. The analyses given below were borrowed chiefly from unpublished archival materials (50; 51; 53), and only analyses 3 and 4 were taken from the work of Dr. Azletsky (35). ↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩

2. Brine strength 7.6° Bé. ↩↩↩↩↩↩↩

3. Brine strength 7.5° Bé. ↩

4. Brine strength 7.5° Bé. ↩

5. Brine strength 7.4° Bé. ↩

6. Brine strength 7.2° Bé. ↩

7. Brine strength according to Baumé 2½°. ↩

8. Brine strength according to Baumé 7.4°. ↩

9. Brine strength according to Baumé 7.6°. ↩

10. Brine strength according to Baumé 7.6°. ↩