F. N. Shakhov, mining engineer,
instructor at the Siberian Technological Institute.

Magmatic Rocks of the Kuznetsk Basin

Introduction

The material for the present work was a collection of igneous rocks gathered by Prof. M. A. Usov in 1923 in the Kuznetsk Basin (20, 95). The various rocks in the collection were taken chiefly during a traverse along the Tom River, which was investigated from the mouth of the Belsu River to the city of Tomsk.

All the material naturally divides into two main parts: 1) igneous rocks associated with the coal-bearing sequence, and 2) effusives of the Devonian deposits. The first group consists of the alkaline basalts of the Saltymakovo Range and the Karakan Mountains, and their hypabyssal analogues of monzonite-essexite composition. The group of Devonian effusives includes albitophyres, various porphyrites and metaphires as part of diagenetized and greenstone-altered phases, in the sense of Prof. M. A. Usov (36, 18--21). To this group may also be assigned the diabases that form a laccolith-like body near the village of Ubiennaya.

The magmatic rocks of the Kuznetsk Basin have long attracted the attention of researchers who visited this region at different times. If one does not count isolated mentions of various igneous rocks in the works of military geologists^1) of the beginning of the nineteenth century, the first descriptions of effusives, though without microscopic treatment, are found in Shchurovsky, who traveled through Altai in 1844 (2). The first microscopic determinations were given by Karpinsky for the diabase rocks of the environs of the Guryevsk works (3, 14--16) and the basalts of the Tom River (3, 32) in 1875. In 1883 there appeared a summary work on the Kuznetsk Basin by mining engineer D. P. Bogdanov, who, in describing the rocks, used the materials of Shchurovsky (4, 200) and Karpinsky (4, 165--166). Only from the 1890s of the last century onward do brief microscopic descriptions of various magmatic rocks appear in works on the study of the Kuznetsk Basin. Such descriptions were given by Derzhavin (5, 114--125; 6, 29--35; 8, 98) for the rocks of the productive sequence and the Devonian. It is of interest that Derzhavin calls Karpinsky’s basalts metaphires (6, 118), proceeding exclusively from the supposed ancient age of the coal-bearing sequence. Subsequent works by cabinet geologists, namely: Venyukov P. (7), Polenov V. (10, 12), Inostrantsev A. (11), and Tolmachev I. (13), likewise do not have the character of special petrographic investigations and at times contain contradictory descriptions for rocks of one and the same outcrop. The only petrographic work is a small article by F. Shnel on diabases in the clayey shales of the environs of the city of Tomsk (15). According to Yanishevsky’s investigations, these diabases cut Lower Carboniferous sediments (16, 83) and, apparently, are distinct from the Devonian effusives described in the present work^2).

^1) Sokolovsky 2, Ivanitsky A., Gerngross 2, Frese A. E., Kulibin, and others. The reports were printed in Gornyi Zhurnal for 1835--1843. For more detail see (9, 218).

^2) Butov N. P. mentions a bedded diabase vein in Lower Carboniferous limestone (19, 146).

Among the subsequent works by investigators of Kuzbass one may note the report of Yanishevsky (14, 10, and 19), who, in defining the rocks, adheres to the names of previous investigators; the work of the Lutugin parties (17, 18, and 19); and, finally, the article by Prof. M. A. Usov on the tectonics of the Kuznetsk Basin, where preliminary determinations are given for the rocks of the collection described here¹.

As is evident from this brief review of the literature, there are no special petrographic works on Kuzbass, and the determinations made by individual geologists are accidental and often contradictory in character. Therefore, in describing the rocks, I considered it necessary, as far as possible, to cite the nomenclature and determinations of previous investigators who have descriptions of the corresponding outcrops or of very similar rocks from other districts of Kuzbass.

In compiling the present work the author made use of the valuable advice and indications of Prof. M. A. Usov, and therefore considers it a pleasant duty to express to him his deep and sincere gratitude.

Magmatic rocks of the productive series.

1. Monzonite-essexites.

These rocks are best exposed on the left bank of the Tom River between the uluses of Kurya and Syrkashev, where they form three small intrusive bodies (sills), occurring conformably with the enclosing argillites of the Balakhonka suite of the productive series of the Kuznetsk Basin (20, 99—100). In addition, outcrops of the same rocks are found along the Tom River in the Yulyel ulus, near the mouth of the Bolshoi Maizas River. Judging from the literature, rocks of this type are encountered rather frequently in the southern and southeastern part of the Kuznetsk Basin. Thus Shchurovsky describes a “diorite resembling black-colored wax” (2, 144), an erupted rock cutting through the coal-bearing series on the Mrassa River, somewhat above the Tatar village of Chuvashka, and calls it now a melaphyre, now an augite porphyrite. It is interesting to note that Shchurovsky (2, 176—177) considered the named rock completely identical with “augite porphyrites” (probably trachybasalts of the Saltymakov Range), brought to him from the section of the Tom River between the mouths of the Nizhnyaya Ters and the Taidon River, and distinct from the “porphyry” from the Nizhnyaya Ters, which, judging from the description, resembles Devonian porphyrites².

Apparently, Derzhavin (5, 114) speaks of the same outcrop on the Mrassa River, 4 versts above the Kameshok ulus. The rock is called diabase, but, judging from the description, it is very close to the monzonite-essexites of the Kurya and Syrkashev uluses. The same author notes three outcrops of similar rocks along the Usa River (5, 116—117). Two of these outcrops occur within the productive series, and the rocks of these outcrops the author, considering them identical with the rocks of the Mrassa, calls diabases. The third outcrop is situated close to the boundary of the productive series, three versts below the mouth of the Chek-Su River. Derzhavin singles out the rocks of this outcrop, calls them melaphyres, and equates them with the basalts of the Karakan Mountains. The form of occurrence of these rocks appears to Derzhavin as “domes amid folded and bent coal-bearing deposits” (5, 117). These same outcrops along the Usa River were described by Tolmachev, who

considers the rocks of one outcrop¹ to be a vitrophyric plagioclase porphyrite (13, 331), and the rocks of the other²—an olivine diabase with biotite and hornblende (13, 332). In both cases the enclosing rocks bear imprints of leaves of Cordaites sp. In the author’s opinion, the rocks occur as sheet-like veins and vary considerably in composition and structure (13, 332), i.e., they are typical hypabyssal formations (37, 13–22). Finally, similar rocks from the left bank of the River Tutuyas, somewhat below the mouth of the River Kyzyr-su, are described by Yavorskii (18, 12) under the name of conta-diabases and are regarded by him as analogous to the rocks of the Syrkashëvo ulus.

In our collection there are samples from three localities: 1) the left bank of the River Tom opposite the Kurya ulus; 2) the left bank of the River Tom somewhat below the Syrkashëvo ulus; and 3) Cape Yulgel, near the mouth of the River B. Maizas. The rocks of all three outcrops are very close to one another both in structure and in mineralogical composition, so that I shall allow myself to dwell in more detail only on the description of the monzonite-essexites of the Kurya ulus, which are represented most fully in the collection, and only briefly note the common features and peculiarities of these rocks from the two other outcrops.

Monzonite-essexites of the Kurya ulus.

Being typical hypabyssal formations, these rocks vary greatly in grain size, color, structure, and mineralogical composition. In the central parts of the body they are variegated, quartz-bearing orthoclase-plagioclase rocks of equigranular, gabbroid structure, with an average grain size of 3.5 mm. In the marginal zones they are dense black-gray rocks, with a porphyritic structure varying in intensity and often weakly expressed, with the potassium-sodium alkali feldspar almost entirely absent and with a sharp decrease, and at times complete disappearance, of quartz. The grain size in the porphyritic segregations ranges from 4.85 mm to 0.16 mm, and in the groundmass from 0.48 mm down to glass in samples directly in contact with the country rock. Contact metamorphism is weakly expressed, but nevertheless the hornfelsing of the argillite is noticeable at approximately 30 meters from the contact. The samples taken characterize the body in the following order: a) sample 39b represents the immediate contact of the sill with the argillite; b) sample 39c was taken about 17 cm from 39b; c) sample 39d—two meters from 39c; d) sample 39e—two meters from 39d; e) sample 39f four meters from 39e; and, finally, f) samples 39g and 39h were taken in the center of the body, approximately 30 meters from the contact.

Sample 39b represents a dense black-gray rock with the finest porphyritic segregations of plagioclase. In some parts of the thin section there are rare, irregularly shaped phenocrysts—aggregates of dirty-yellow, sometimes faintly greenish color, consisting of plagioclase prisms averaging about 1.5 mm in size. Associated with them are also irregularly shaped and approximately equally sized accumulations of quartz.

Under the microscope, in thin section, the porphyritic structure of the rock is revealed very sharply. The porphyritic segregations are represented exclusively by plagioclase, if one does not count the numerous quartz phenocryst-aggregates which, as we shall see below, are a formation of a different order.

Plagioclase (Table I) is usually in moderately elongated, more rarely short-columnar prisms, serially varying in size from 1.84 mm to 0.16 mm. Accumulations of ophytes of arranged prisms are observed. Alterations are very widespread, consisting in sericitization and, in rare cases, in the formation—

replacements of chlorite and epidote along the periphery of the grains. It should be noted that the most altered are the largest phenocrysts, sometimes passing wholly into sericite, and less altered, sometimes even quite fresh, are the small crystals¹. The same may be said of the glass inclusions, which are most strongly developed in the largest crystals and, undoubtedly, are connected with the main mass of the rock, as may readily be verified from Fig. 1. These phenomena, as well as the forms of corrosion often observed in the phenocrysts, convincingly indicate a comparatively high capacity for assimilation by the groundmass. The dusty coating is very weakly developed. There is no zoning. Cleavage is not displayed. More often an andesine-type moderate polysynthetic twin striation is observed, but simple twins also occur occasionally.

Table 1.

BXg	BXp	BXm	2V	Growth plane	No. of plag.	Twin law and features of the crystal
75	88	15	+80° +84°	(001)	30	Manebach law. Phenocrystal 1.24 mm long. Very large number of glass inclusions.
70.5	79.5	22.5	—	(010)	38	$\perp\ [100]$ $(010)$ Cleavage 1.84 mm long.
72	79.5	21	+89°	(0.0)	38	$\perp\ [100]$ $(010)$ Short-columnar prism 0.68 mm long.

The plagioclase numbers are given according to the twin diagram of V. V. Nikitin (30).

Quartz is sometimes found in small xenomorphic, rounded grains with fringed edges. It is usually present in aggregates of hornfelsic structure with the most capricious irregular outlines. Figure 2 depicts one such formation, whose length is 1.24 mm. The internal boundaries of the individual grains are usually smooth or, more rarely, rectilinear. The external boundaries are fringed. Sometimes in these aggregates bay-like inlets of glass are observed, with which biotite is definitely associated, appearing in this thin section only in quartz accumulations (Fig. 3). It must be supposed that, in the overwhelming majority of cases, the quartz represents altered, metamorphosed inclusions of the country rock assimilated by the groundmass, while the biotite is a new formation during the process of this metamorphism. It is interesting to note that a very similar phenomenon was observed by A. V. Lavrsky (24, 69) in the traps of the interfluve of the Lena and Yenisei, where fused sharp-angled fragments of quartz from the country rock produce glass formation with the appearance, as a product of reaction between quartz and the magmatic solution, of augite rims. One may think that the biotite in the present case will be a similar formation, especially since, as we shall see below, glass in the groundmass is more often observed near quartz aggregates.

The groundmass is heterogeneously recrystallized in different parts of the thin section. Usually it is a feldspathic mass of microfelsitic structure, brownish-gray in color from numerous dots of crystals of iron ore, apparently ilmenite, judging by the somewhat elongated forms of the largest

individuals. Small ilmenite crystals are not uniformly scattered throughout the groundmass, but are often grouped in clusters—accumulations around the smallest grains of quartz and feldspar. Around large phenocrysts, and also along the periphery of the quartz aggregates described, accumulations of ilmenite form a kind of halo, consisting of fine ilmenite microlites in a glassy groundmass. It should be noted that the glass is most often associated with portions of the groundmass adjoining the porphyritic segregations of plagioclase or fragments of quartz. Such a regular distribution of glass in the rock definitely indicates conditions little favorable for crystallization at the moment when the magma dissolved the phenocrysts and fragments of the host rock. The termination of ilmenite needles on the surfaces of phenocrysts and inclusions by the cooling silicate melt is apparently connected with this same circumstance.

Taking into account the presence of facts indicating processes of assimilation in the specimen described, it can in no case be regarded as a normal igneous rock, but most likely as an endocontact variety. The composition of the plagioclases, as we shall see below, is also in agreement with this latter proposition, being more acidic than might have been expected for the periphery of this body.

Specimen No. 39-c. A dark-gray rock of porphyritic structure with a fine, but distinctly granular groundmass. There are more porphyritic segregations than in the preceding rock, but in size they differ less sharply from the groundmass, and pass imperceptibly into it, varying in size from 1.45 mm to 0.22 mm. The average grain size of the groundmass is approximately 0.15 mm.

The porphyritic segregations consist of plagioclase, pyroxene, and a brown mineral replacing the latter, resembling amphibole. In addition, here and there accumulations of idiomorphic, well-bounded quartz and calcite are noticeable; these formations essentially do not belong to the porphyritic segregations, but represent fillings of miarolitic cavities.

Plagioclase (Table II) predominates, both in size and in number of crystals, over the phenocrysts of augite. It usually occurs as prismatic individuals, but rhomboid tablets are sometimes encountered. It is always zonal and strongly sericitized, with deposition along cleavage cracks, as well as along the boundaries of the zones, of brown aggregates of the highly polarizing brown mineral mentioned above (Figs. 4 and 5). Processes of such replacement are observed only in large plagioclase crystals that are more basic in composition.

Table II.

No. in order	BNg′	BNm.	BNp.	2 V	Extinction plane	No. plag.	Twinning law and features of the crystal
1	85°	28°	63°	+80°	?	53	⟂ (021). Very zonal sericitized tablet, 0.90 mm long.
2	31°	77°	62°	—	(010)	49	⟂ (010). Small prism, smaller than the preceding, fresh.
3	57°	71°	55°	+80°; +80°	(010)	63	(101). Central part of a large sericitized prism. Length 1.44 mm.
4	61°	55°	46°	+82°; +72°	(010)	49	(001). Periphery of the preceding crystal.
5	31°	61.5°	78.5°	+80°	(010)	49	⟂ (010). Small crystal, the same as No. 2.
6	42°	59°	65°	+86°	(010)	69	⟂ (010). Large tablet of type No. 3.
7	32°	61.5°	76°	+82°	(010)	50	⟂ (010). Peripheral part of the preceding.

In addition, for one of the large crystals the magnitude of birefringence was determined for the very outermost zone, and the following figures were obtained: Ng—Np = 0.0065; Ng—Nm = 0.0033; 2V = +89° (by calculation). It is possible that the outer shell of the plagioclases may reach No. 40¹.

Thus, two generations of plagioclases may be distinguished in the porphyritic segregations. To the first belong the large altered crystals with a core composition from No. 69 to No. 53 and a peripheral part of No. 49 and more acid. To the second belong small, fresh prisms, rarely zoned, with a core composition of No. 49.

Pyroxene is observed in the porphyritic segregations less commonly than plagioclase. The size of its grains varies, but they never attain the dimensions of plagioclase prisms. The color is pale violet. It is usually zoned and gives beautiful twins. More often it occurs in fused, rounded grains with a rim of a brown pleochroic substance, the nature of which, apparently, is very close to an amphibole-like mineral filling cleavage cracks in the plagioclases. At times large pseudomorphs of this substance after pyroxene are encountered, and then one clearly sees a fibrous mineral with relict inclusions of augite, surrounded by a rim of material somewhat more darkly colored than the rest of the groundmass, with less vivid polarization colors and pleochroism (Fig. 8). Pyroxene, like plagioclase, also varies in composition and probably likewise represents two generations, as is indicated by occasional overgrowths of a strongly fused augite crystal by another, optically differently oriented individual (Fig. 6). Measurements of individual zones of the overgrowth of a phenocryst (Fig. 7) gave the following results. Zone a: 2V = +44°; CNg = 43.5°. Zone б: 2V = +52°; CNg = 48°. Zone в: 2V = +57°; CNg = 49°. The comparatively small angle of the optic axes compels one to assign the pyroxene to calcium-poor pyroxenes of Wahl (55, 110), the amount of calcium increasing from the center toward the periphery. The large extinction angle is probably due to the titanium content (56, 515), as is also indicated by the pale violet color.

A brown mineral, usually forming pseudomorphs after pyroxene, is extremely widespread in the rock. Its color varies from pale yellow to dark brown, almost black. In the lightest specimens the pleochroism is always more vivid—just as the high polarization colors also stand out more vividly. In these same cases one can very clearly observe a rather distinct and sharply expressed cleavage in one direction, with straight extinction, or extinction perhaps close to it. It is quite possible that the dark-colored specimens belong to individuals cut along the cleavage plane, but, apparently, besides this, the dark-brown color also depends on the following circumstance: the chief peculiarity of the mineral is the heterogeneity of its structure, expressed in bands—patches of brown ferruginous material which clog the crystal and darken its optical properties. The high relief, high birefringence, and heterogeneity—the spotted character of the mineral—strongly recall the basaltic hornblendes described by Rosenbusch (50, 235–236) under the name syntagmatite, characteristic of basic alkaline rocks. But, on the other hand, a single cleavage system with straight extinction closely recalls iddingsite (50, 159). It is interesting to note that syntagmatite, as well as iddingsite, contains chemically bound water in the amount of 2.5%, and thus may be a mineral formed under conditions similar to those of iddingsite.

The material at our disposal does not make it possible, nor give us the right, to name this mineral definitely, but it does allow us to approach to some extent the clarification of the conditions of its formation. We have already mentioned earlier that the brown mineral into which pyroxene passes is deposited along

along cleavage cracks and lines of zoning in the porphyritic phenocrysts of plagioclase. Moreover, it must be noted that the usual form of its external outlines is paw-like, split, with long tails—strands penetrating into cracks and into the boundaries of neighboring minerals. It follows naturally from this that the formation of this mineral took place at a time when the main components of the rock were in a solid crystalline phase. In the present case the main mass of the mineral forms pseudomorphs after pyroxene, probably at a moment close to the filling of the miarolitic cavities by quartz and calcite. Evidence for the latter proposition is provided by miarolitic cavities filled with idiomorphic quartz and our brown mineral (Fig. 26), for which, for convenience of description, we shall retain the name iddingsite. The association of iddingsite and quartz in the miarolitic cavities, as well as its capacity for migration and replacement of other mineral components of the rock, allow one to think that the initial material for its formation is a residual siliceous solution, to which the substance of the minerals being replaced is admixed. Thus, in the present case we are dealing with a process of autometamorphism¹, complicated by a process of replacement—a phenomenon to which it is appropriate to give the name autometasomatism.

Quartz is always encountered together with calcite, and in very small quantity at that. It usually has excellent crystallographic boundaries (Fig. 9). Calcite rarely has rectilinear outlines and always fills the spaces between quartz crystals. Minerals adjoining accumulations of quartz and calcite always possess well-pronounced rectilinear boundaries, and the crystallographic faces appear only on that side of the mineral which borders the former miarolitic cavity (Fig. 18). The filling of cavities by quartz and calcite was accompanied by partial metamorphism of the rock, as indicated by thin scales of completely fresh biotite along the margins of these formations, as well as by a more pronounced sericitization of the nearest prisms of plagioclase.

The groundmass is of ophitic structure and consists of laths of plagioclase, augite, iddingsite, and a large quantity of long, ophitically arranged needles of ilmenite; in places accumulations of pyrites are observed. The interstices of the plagioclase laths are often filled, instead of pyroxene, by a variegatedly polarizing, inhomogeneous iddingsitic material. These formations are especially strongly developed near the pyrites. Apparently the latter were deposited in the rock in the latest stages of its life and possibly contributed to the formation of iddingsite.

The pyrites form irregularly shaped branching aggregates with accumulations of iddingsite and biotite. Their pinkish coloration in daylight by reflected light recalls pyrrhotite or nickel pyrites. Pyrite also occurs.

The chemical analysis of the rock gave the following results: SiO₂—51.10%; Al₂O₃—17.76%; Fe₂O₃—5.57%; FeO—7.53%; MgO—3.58%; CaO—7.15%; Na₂O—2.44%; K₂O—1.14%; H₂O—0.50%; loss on ignition—1.19%. The rock symbol according to Levinson-Lessing is—

\[ \frac{1.80R}{1.7\alpha}\tag{27}, \]

which, according to his chemical classification, defines our rock as diorite (26).

Specimen 39-d. A dark-gray rock, somewhat lighter than the preceding one, almost even-grained, with a very weakly expressed porphyritic structure. The porphyritic phenocrysts are represented only by plagioclase, whose prisms, varying serially in size from 4.85 mm to 1.13 mm, pass imperceptibly into the groundmass. The groundmass consists of plagioclase, pyro-

pyroxene, iddingsite, biotite, ilmenite, sphene, quartz, and calcite; moreover, the last three minerals occur rarely and are not essential constituent parts. Of all the components composing the rock, only plagioclase possesses crystallographic boundaries and, in combination with the pyroxenes, imparts an ophitic character to the structure of the rock. The grain size of the groundmass varies within the limits from 1.13 to 0.11 mm.

Plagioclase is the same as in 39c. In the porphyritic segregations it is sericitized and has a greater content of the anorthite molecule than the plagioclase of the groundmass (Table III).

Table III.

No. in porphyr.	BNg	BNm	BNp	2V	Composition plane	No. plag.	Twinning law and crystal features
1	58	75	37	+86°	(010)	63	[001]. Large phenocryst, 4.85 mm long. Sericitized, zonal. Inner part.
2	73	34°	62°	+88°	(010)	63	Same $\perp \dfrac{[001]}{(010)}$. Second pair of twins.
3	63.5	57	45	+74° +74°	(010)	50	[001]. The same twins as in No. 1, but the outer part.
4	77	46	47	+72°	(010)	50	$\perp \dfrac{[001]}{(010)}$. Thin lath of the groundmass.
5	62.5	57.5	43°	+74°	(010)	50	[001]. Broad tabular crystal of the groundmass, zonal.

Pyroxene occurs in very small grains. It appears in the same way as in 39c, with the difference that it is no longer found in the porphyritic segregations. A certain distinction of the present rock from 39c is the presence, in fairly considerable quantity, of biotite. Pleochroic in light-yellow tones in the inner parts of the crystal, the biotite has a green coloration in the peripheral parts. The birefringence changes very little in connection with the change of brown coloration to green. In the thin section, green biotite predominates. In quantity it is only slightly inferior to augite. Iddingsite is always associated with biotite and, as may be seen from the character of the aggregate clusters of these minerals (Fig. 10), partly replaces it and is formed at the expense of biotite. Thus, it must be supposed that iddingsite can replace all the pyroxenes of the given rock, and the absence of biotite in the groundmass of the preceding rock can be easily explained by its complete replacement by iddingsite.

Ilmenite is present in large quantity, in needles up to 0.93 mm long. In places it is altered to leucoxene. Sphene sometimes appears. Miarolitic cavities filled with calcite and quartz occur in the same way as in 39c. A certain distinction is the presence of quartz grains and their aggregates which are not accompanied by calcite, but always preserve rectilinear angular boundary forms (Fig. 11). These formations seem to play the role of predecessors of the pegmatitic residual quartz–feldspathic mass, strongly developed in the parts of the intrusion located nearer the center.

Sample 39e. In connection with the greater individualization of feldspar, the rock has a dark-gray coloration, though lighter than 39d. Structur-

macroscopically equigranular. Under the microscope, however, one can still distinguish rare porphyritic segregations of plagioclase No. 62, zonal and twinned according to the Carlsbad law. The size of these prisms is small and reaches approximately 1.87 mm. The grains of the groundmass are larger than in the preceding rock and are rarely less than 0.45 mm.

The composition of the groundmass differs somewhat from that of the preceding rock. The principal difference is the comparatively large amount of quartz, appearing, as also in 39-d, but without calcite. In the present case the formation of quartz is associated with other minerals, and—we must suppose—we are dealing with a stage transitional in character from magmatic to pneumatolytic. The point is that biotite crystallizes simultaneously with quartz; i.e., one can often see the penetration of thin threads of biotite into quartz crystals, the aggregates of which no longer have outlines characteristic of miarolitic cavities (Fig. 12). A certain structural difference from the preceding rocks is the predominance of short columnar prisms—tablets of plagioclase, which gives the structure a dioritic character. Except for plagioclase and ilmenite, all the remaining components have boundaries close to allotriomorphic.

Specimen 39-f. A dirty-gray, with a faint brownish tint, medium- and even-grained rock. The grain size rarely exceeds 1.50 mm and is not less than 0.60 mm, so that with the unaided eye one can distinguish the grayish-white parts of feldspar and the dark-colored components, sharply lustrous on cleavage planes. Porphyritic segregations are not observed even under the microscope, and the rock has a structure approaching ophitic. In mineralogical composition it differs somewhat from the preceding one. The predominant component is plagioclase in ophitically arranged short-columnar prisms, in the interstices of which are located augite, hornblende, iddingsite, biotite, devoid of crystallographic boundaries, a small amount of alkali feldspar and quartz, pegmatitically intergrown with one another, and a rather considerable amount of apatite, associated with biotite and iddingsite. The relations of the pyroxenes and the pegmatitic residue are somewhat different. The former crystallize either by penetrating or partly resorbing the plagioclase, whereas the latter occupy rectilinearly bounded, often triangular areas between the plagioclase prisms. The ophitic character of the structure is emphasized by long needles of ilmenite intersecting at various angles. Calcite has been noted here and there.

The composition of the plagioclase is apparently the same for all crystals of the rock (see Table IV) and corresponds to the composition of the plagioclases of the groundmass of the preceding rocks. It is separated out soon after the pyroxene, since it often resorbs the latter (Fig. 14), dissolving in turn simultaneously with augite and hornblende (Figs. 13 and 14).

Table IV.

No. in order	BNξ	BNm	BNp	2V	Plane of intergrowth	No.	Twin law and features of the crystal
1	79°	52°	40°	+78°	(010)	12	⟂ [001] / (010). Central part of a very zonal crystal, somewhat distinguished by size.
2	65°	56°	45°	+74°	(010)	48	[001]. Fine-grained small veinlet.
3	79°	47.5°	41°	+81°	(010)	46	⟂ [001] / (010). Short-columnar prism, weakly zonal, of medium size.
4	55°	41°	72°	—	—	50	Cleavage along (001) in the preceding crystal.

Titanian augite is pale violet, and is often overgrown along the margins by greenish-brown hornblende. In its constants it approaches magnesian titanium-bearing pyroxenes. \(2V\) varies from \(-40^\circ\) to \(-42^\circ\). \(CNg\)—from \(39^\circ\) to \(48^\circ\). It is interesting to note that the transition of augite into hornblende is often accompanied by the simultaneous formation of biotite (Fig. 15). Sometimes the dissolution of pyroxene proceeds so far that only small islands of irregular form remain of it among an aggregate of hornblende, biotite, and iddingsite (Fig. 16).

Hornblende more often appears as an outer rim on pyroxene, but occasionally separate brown crystals with a faint greenish tint are also observed. In its constants it approaches ordinary hornblende. \(CNg\ 18^\circ\)—\(20^\circ\). Pleochroism: along \(Ng\)—pale greenish brown, along \(Np\)—light yellow. Specimens very weakly colored in light-brown and even bluish tones occur.

Iddingsite predominates over the other components of the rock. Most often it is associated with small fragments of biotite, which has partly passed into it (Fig. 17).

Quartz occurs in two forms: filling, together with calcite, miarolitic cavities, and, together with calc-sodic feldspar, in pegmatitic intergrowth. Calcite sometimes alone, without quartz, fills rectilinearly bounded cavities (Fig. 18).

The calc-sodic feldspar is triclinic. It is rarely found in crystals free from quartz intergrowths, and in such cases is always sharply xenomorphic with respect to all minerals except quartz, which always separates either after it or simultaneously with it (Fig. 19). \(2V = -54^\circ\).

\(B \perp (001)\ Ng = 87^\circ;\ BNm = 10^\circ;\ BNp = 81^\circ.\)

Specimens 39h and 39g represent rocks entirely identical in variegated coloration. White spots of feldspars are indistinctly distinguished among black-gray accumulations of dark-colored components. At first glance the rocks have an even-grained gabbroid structure, and only under the microscope is a weakly expressed hypidiomorphic structure detected. The mineralogical composition is the same as in the preceding rock, if one does not count the unusual abundance of zircon inclusions in biotite. The grain size in 39g ranges from 4 mm to 1.4 mm, and in 39h from 4 mm to 3.4 mm.

Plagioclase, as is evident from Table V, is somewhat more acidic than in the preceding rocks. In the present case it crystallizes simultaneously with pyroxene (Fig. 20). It is always idiomorphic with respect to all the other minerals of the rock. It is fine-zoned; kaolinized and sericitized. It is often mantled by calc-sodic feldspar (Fig. 21).

Pyroxene is very rarely found in individualized crystals, and usually intergrows with plagioclase (Figs. 20 and 22). It is always overgrown along the margins by amphibole. An isolated pyroxene crystal has the constants: \(2V = +52^\circ\) and \(CNg = 44^\circ\). A patch in plagioclase (Fig. 20): \(2V = +58^\circ\) and \(CNg = 35^\circ\). It must be supposed that in the first case we have a magnesian pyroxene, which crystallized before the plagioclase. Together with the plagioclase, however, there crystallized a mineral enriched in calcium and poorer in titanium.

Hornblende occurs more often as a border on pyroxene crystals, but occasionally separate independent individuals of it can also be observed. Its color is very variable; more often it is composed of pale bluish and brown tones. \(CNg = 28^\circ\)—\(31^\circ\); \(2V = -60^\circ\). Judging by the small angle of the optic axes and the large extinction angle, the hornblende in the present case apparently approaches kataphorite (50). Probably we are dealing with a series of gradual transitions from ordinary hornblende (specimen 39f) to alkaline hornblende, in connection with an increase in the alkali content in the central parts of the sill.

Table V.

No. of specimen	No. in order	BNg.	BNm.	BNr.	2V.	Intergrowth plane	No.	Twinning law and features of the crystal
39g	1	24.5	66°	85.5°	+78°	(001)	42	$\perp \dfrac{[100]}{(001)}$. Central part of a large fine-grained plate with intergrown twins.
”	2	30°	62	80°	$+78^\circ$ $+84^\circ$	(001)	47	$\perp \dfrac{[100]}{(001)}$. Fine-grained plate with complex polysynthetic twins.
”	3	27°	63°	82°	$+84^\circ$ $+88^\circ$	(001)	44	$\perp \dfrac{[110]}{(001)}$. Same as No. 1.
”	4	33°	58°	80.5°	+76°	(001)	48	$\perp \dfrac{[100]}{(001)}$. Sprouted by augite crystal.
”	5	62°	33°	73	—	—	45	Cleavage plane along (001) in the preceding crystal.
39h	6	27	63°	83°	$+78^\circ$ $+81^\circ$	(010)	43	$\perp(010)$. Fine-grained simple twin, overgrown by calcium-sodium feldspar.
”	7	23°	68°	85°	$+82^\circ$ $+84^\circ$	(010)	40	$\perp(010)$. Crystal similar to the preceding one. Intergrowth. Intergrowth I and II.
”	8	69.5°	12.5°	55°	+80	(010)	40	$[001]$ Intergrowth II and III.
”	9	80	56.5°	35.5°	—	(010)	39	$\perp \dfrac{[001]}{(010)}$. Intergrowth III and I.
”	10	61	29.5°	76.5	—	—	42	Cleavage plane along (001) in individual I.
”	11	22	69°	85	—	—	40	Cleavage plane along (010) in individual I.

Biotite is always fresh, in bright red pleochroic tones; it abounds in inclusions of zircon and apatite with sharply expressed pleochroic halos. In addition to biotite, thin crystals of colorless mica were observed here and there, associated, like biotite, with iddingsite.

Potassium-sodium feldspar occurs rarely, as separate grains. Usually it either overgrows plagioclase, or crystallizes in granophyric intergrowths with quartz. Sometimes, within the micropegmatite field, one can see rather large, very resorbed crystals of this mineral (Fig. 55), precipitated, apparently, before the mass dissolving it. $2V = -50^\circ$; $B \perp (001)$ Ng $=-80^\circ$; BNm $=12^\circ$; BNr $=83^\circ$. Probably a sodium-rich triadic alkali feldspar close to anorthoclase. According to Winchell (57, 722), it contains 60% of the anorthoclase-albite molecule.

Chemical analysis of the rock gave the following results: $\mathrm{SiO_2}=56.16\%$; $\mathrm{Al_2O_3}=17.30\%$; $\mathrm{Fe_2O_3}=4.94\%$; $\mathrm{FeO}=6.68\%$; $\mathrm{CaO}=5.16\%$; $\mathrm{MgO}=1.80\%$;

$\mathrm{Na_2O}=3.78\%$; $\mathrm{K_2O}=4.22\%$; $\mathrm{H_2O}=0.61\%$ and loss on ignition—$0.79\%$.

The rock symbol according to Levinson-Lessing is: $\dfrac{1.67dR}{1.99a}$. In the present case the rock exactly coincides with the essexites (26).

Taking into account the changes in the structure and mineralogical composition of the rocks described, we can divide them into three groups with more or less gradual transitions between them. The first group includes rock 39b, with noticeable traces of assimilation of the country rocks and a sharp transition to the more basic formations of the second group—sample 39c. Rocks of the second group always possess a well-expressed porphyritic structure. The phenocrysts are represented chiefly by plagioclase and, only in the marginal members close to the contact, by pyroxene. With increasing distance from the contact, the number of porphyritic segregations decreases and the sodium content in the porphyritic plagioclase segregations increases; but, in comparison with the rock of the first group (39b), the plagioclases are considerably richer in the anorthite molecule.

The first group has only a very small extent from the selvage, since already 17 cm from 39b a sample of the second group—39c—was taken; beginning with it, the composition of the rocks changes continuously in the direction of enrichment in silica. The thickness of the rocks of the second group slightly exceeds 4 meters. The greatest dimensions are possessed by the third group of equigranular rocks, which, in the composition of their plagioclase, are very close to the main mass of the rocks of the second group, but, in comparison with the latter, are enriched by abundant nests of quartz-feldspathic residuum. It must be pointed out that within this group of rocks, with increasing distance from the contact, a weak but continuous increase in acidity is nevertheless observed, which is very well illustrated by comparison of the composition of the plagioclases in samples 39g and 39h, taken at a distance of 30 meters from the selvage and very close to each other. In 39g the average composition of the plagioclase is No. 45, in 39h—No. 40.

The formation of the rocks described cannot be explained solely by crystallization differentiation of the magma. The porphyritic structure, zoned pyroxenes, and other indications of constrained conditions of crystallization observed in the second group of rocks make it possible to regard these rocks as the closest in composition to the first portions of cooling of the intruding magma. From this basic group, changes proceed in the direction of increasing acidity both toward the selvages and toward the central parts of the sill.

The increase in acidity toward the contact may be explained either by assimilation of the country rock or by settling of the magma. Since we are dealing with contacts of the hanging wall, the latter explanation appears possible. However, the signs of assimilation in rock 39b, as well as the increase in acidity beginning after 17 cm, and not its decrease at the base of the sill, as would be expected if a process of settling were assumed, compel us to abandon this explanation and to conclude that, in the formation of 39b, assimilation by the magma of the country rock played an essential role¹.

Of very great interest in this respect is the work of Bowen on the study of assimilation processes in the norites of Sudbury (40). In Fig. 23 his diagram is placed, showing the change in the composition of the norites in relation to distance from the footwall. It is not difficult to see that the character of the change in the composition of the norites is exactly the same as in our essexite rocks, despite the fact that in our case we are dealing with the contact of the hanging wall. The sharp decrease in acidity on the segment AB corresponds fully to the transition from 39b to 39c over a distance of 17 cm and once again indicates

the complete impossibility of explaining the formation of 39 b by the settling of magma¹. The further increase in acidity in the segment BC fully corresponds to the change in the composition of groups II and III of our rocks. Taking as the primary composition of the magma the average analysis of the rocks adjacent to the contact, Bowen, by comparing the average composition of the whole diagram with the supposed primary one, concludes that the formation of the norites was preceded by the assimilation by the magma of a large quantity of country rocks (38% of the final composition), in the presence of extremely weak contact metamorphism.

Bowen’s work was discussed by Fenner (49) and Bowen (43). Like them, we cannot agree with the computational part of Bowen’s work, but we would like to note one fact to which, during the discussion, very little attention was paid. It is interesting that even Bowen makes no attempts to explain the sharp decrease in acidity in the segment AB. It seems to us that, since this phenomenon is most easily explained by the process of assimilation, it therefore represents a very weighty argument for characterizing and proving the capacity of the magma to assimilate country rocks. If we assume that the increase in acidity toward the salband is explained by the process of assimilation, then point B on the SiO₂ curve (Fig. 23) must belong to a rock with a chemical composition close not to that of the primary intruding magma, but, as we indicated above, to the first sufficiently basic rock of cooling. Probably the neglect of this circumstance is the main reason why Bowen’s attempt—to calculate the dimensions of assimilation, which in this case is characterized by an increase in acidity over a comparatively small segment of the curve from B to A—proved unsuccessful. In addition, apparently, fluctuations in the composition of the rock do not always occur as simply as is shown in Fig. 23. I have reproduced here Bowen’s second diagram for another part of the norite body (Fig. 24), where, apparently, assimilation was more energetic, and before reaching its minimum the curve for SiO₂ intersects several maxima and minima of the second order. Such fluctuation in composition can be explained only by the process of assimilation, and a careful study of the marginal zones of similar hypabyssal bodies may provide very valuable and interesting material for elucidating the role of assimilation in the process of magmatic differentiation.

The process of crystallization of rocks of the third group proceeded somewhat more simply. We saw, in describing the corresponding specimens, that in their composition these rocks approach the composition of the main mass of rocks of the second group, and in some cases are even more acidic than they, judging by the number of the plagioclase and the noticeable increase in quartz. In addition, from consideration of the structural relations of the various minerals we have occasion to be convinced that the features of incomplete discontinuous reactions (series: augite ⇄ amphibole ⇄ biotite) and continuous reactions (zonal plagioclases) of Bowen’s series (42) are very widespread and sharply expressed in our rocks. Naturally, therefore, the formation of rocks of the third group can easily be placed within the framework of crystallization differentiation, understanding the process of crystallization as a combination of Bowen’s series, as a result of which an accumulation of active quartz–feldspar residue is formed.

Monzonite-essexites of the Syrkash Uluus.

The rocks of the Syrkash Uluus were described by Tolmachev (13, 430) under the name of quartz-olivine diabases. In my material, olivine was not observed, and, probably, the abundance of iddingsite, in the sense adopted by me for these rocks, was the reason for such a designation. According to the mineralogical

in composition, the rocks are quite identical to the monzonite—essexites of the Kura ravine. A certain difference is noticeable in that these rocks attain coarser-grained varieties (7.7 mm), are rich in sulfides, and contain more acidic (Table VI) plagioclase numbers, which, it must be supposed, is connected with the greater thickness of the sill.

Table VI.

Sample No.	Distance from contact	\(BXg\)	\(BXm\)	\(BXp\)	\(2V\)	Cleavage plane	Plagioclase No.	Twinning law and features of the crystal
36d	60 cm	\(37^\circ\)	\(57^\circ\)	\(74^\circ\)	\(+75^\circ\) \(+78^\circ\)	(001)	55	\(\perp [100]\). Phenocryst 4.21 mm long with the grain size of the groundmass 0.08 mm.
36c	3 m	\(68^\circ\)	\(45^\circ\)	\(53^\circ\)	\(+82^\circ\)	(010)	42	[001]. Marginal zone of a phenocryst 1.45 mm long.
36c	3 m	\(30^\circ\)	\(67^\circ\)	\(80^\circ\)	\(+72^\circ\) \(+76^\circ\)	(010)	48	\(\perp (010)\). Core of a lath of the groundmass. Length—0.84 mm.
36c	3 m	\(22^\circ.5\)	\(68^\circ\)	\(83^\circ\)	—	(010)	40	\(\perp (010)\). Zonal lath of the groundmass, length—0.54 mm.
36c	3 m	\(29^\circ\)	—	—	\(+77^\circ\)	—	47	Cleavage along (010). Lath of the groundmass.
36b	25 m	\(70^\circ\)	\(20^\circ\)	\(84^\circ\)	\(90^\circ\)	—	36	Cleavage along (001) in a large crystal 7.7 mm long.
36b	25 m	\(71^\circ\)	\(21^\circ\)	\(84^\circ\)	\(90^\circ\)	—	37	Cleavage along (001) in a grain 3.21 mm long.
36b	25 m	\(67^\circ\)	\(24^\circ\)	\(84^\circ\)	—	(001)	39	\(\perp (001)\). A prism like the preceding one.

Pyroxene is richer in calcium than in the rocks of the Kura ravine. \(2V\)—from \(+50^\circ\) to \(53^\circ\). \(cNg\)—from \(41^\circ\) to \(48^\circ\). Amphibole, as in the rocks of Kura, appears only in the coarse-grained varieties. \(2V = -74^\circ\), \(cNg\)—from \(15^\circ\) to \(19^\circ\). Pleochroism: along \(Ng\)—dirty greenish-brown; along \(Nm\)—the same; along \(Np\)—pale yellow. Potassium feldspar was observed only in 36b; in comparison with the anorthoclase of Kura it is somewhat richer in K. \(2V = -64^\circ\); \(B \perp (001)\), \(Ng = 88^\circ\); \(BNm = 9^\circ\), \(BNp = 82^\circ\).

Quartz, calcite, biotite, ilmenite, and iddingsite occur in the same way as in the rocks of the Kura ravine. A certain peculiarity of these rocks may be considered the presence of sulfides (pyrrhotite and chalcopyrite), always accompanied by the formation of sericite, chlorite, epidote, and sphene as products of the alteration of the constituent parts of the rock¹. Finally, it is necessary to note certain features in the structural interrelations of quartz and feldspars. More often quartz occurs in pegmatitic intergrowth with alkali feldspar. In this case the quartz intergrowths possess rectilinear boundaries—

intergrowths. But sometimes one can observe quite clearly fine, irregularly bounded (Fig. 25) intergrowths, similar to myrmekite ingrowths of quartz in plagioclase. Such a difference in the structural relations of quartz with the feldspars can be explained by the degree of similarity of the spatial lattices of these minerals (22), and makes it fairly easy to distinguish the plagioclase intergrowths of quartz from micropegmatitic ones. Very often one can observe the introduction of myrmekitic material into idiomorphic crystals of plagioclase (Fig. 26). Bearing in mind the poverty of our rocks in potassium, one cannot but agree with Svitálsky, who observed similar phenomena in the monzonites of the Tsipikan River (33, 139), that we are dealing with a double eutectic of quartz–plagioclase¹.

Monzonite-essexites of Cape Yulgel.

The exposure has been traced for a distance of 30 meters. The rock is very well developed in structure and nowhere attains the grain size of the formations described above. In the collection there is only one specimen (No. 45) of a medium-grained gray rock, approaching 39e in external appearance. The very weakly developed porphyritic structure compels one to assign it to the transitional member between groups II and III of the rocks². The structure may be called serial-hypidiomorphic. The composition of the rock differs from 39e only in the greater quantity of pyrites and in the almost complete transition of the dark-colored components into chlorite and epidote. Miarolitic cavities are present. Measurements of the plagioclases gave the following results (Table VII).

Table VII.

BNg	BNm	BNp	2V	Plane of intergrowth	No. of plag.	Twin law and features of the crystal
21	66	83.5	+82°	(010)	42	⟂ (010) Sericitized large crystal.
70	24	78	—	(0,0)	39	⟂ \[100\] (010) A long, very strongly sericitized prism; in size closer to the main mass than the preceding crystals.

In the course of investigation of the Kuznetsk Basin, various names were given to the rocks described by us. Shchurovsky (2, 144) and Bogdanov (11, 200) called them melaphyres and augite porphyrites; Derzhavin (5, 114—117), diabases; Tolmachev called the rocks of the Ulus of the Kury a quartz diabase (13, 430), and those of the Ulus of Syrkashev—quartz-olivine diabases; and, finally, Yavorsky—congadiabases (18, 12). Taking into account the alkaline character of the rocks described, we cannot agree with any of the names listed. Closest of all to our rocks are, on the one hand, the essexite diabases of Crimea described by Meister (29), and, on the other, the monzonites of the Tsipikan River described by Svitálsky (33). Since our rocks have not undergone greenschist alteration³, there is no need to use the term diabase, by which rocks that have undergone this alteration are most often under-

in composition, the relatively low potassium content and the abundance of quartz in the rocks of the central parts of the sills make it necessary to prefer a double name—monzonite–essexites.

2. Alkaline basalts.

These rocks occur as sheets among the upper horizons of the coal-bearing sediments (20, 109 and 19, 150) and, together with the latter, being dislocated into a gently synclinal fold, form the well-known “melaphyre horseshoe,” the southern part of which bears the name of the Karakan Mountains, and the northern part—the Saltymakovo Mountains.

These rocks were known already to Shchurovsky (2, 176–177), who took them for “augite porphyries” and considered them analogous to the monzonite–essexites of the Mrasy River. The first microscopic study of them was made in 1875 by Karpinsky (3, 32–33), who called them basalts. This name did not remain in the literature for long. In 1893 Derzhavin (5, 118–119), having in mind the Paleozoic age of the coal-bearing deposits, renamed the basalts melaphyres, and in 1901 Polenov (12, 297)—paleobasalts. The name melaphyre has remained attached to these rocks until the very recent past (19, 150), and only Prof. M. A. Usov (20, 110) in his latest work on the Kuznetsk Basin pointed out their trachydoleritic character. Since in the broad petrographic literature melaphyres are understood to be diagenetized analogues of alkaline (25, 759 and 28, 277) or normal basalts (36, 17), we cannot accept the term melaphyre as suitable for our rocks, the study of which has revealed no appreciable traces of diagenesis. Moreover, as we shall see below, the distinctly expressed alkaline character of these formations compels us to regard the name alkaline basalts as more appropriate for them.

The collection contains specimens of alkaline basalts from the following localities: Skala Babii Kamen¹—the outcrop of the southern limb of the syncline (No. 92), and the Saltymakovo Mountains—the northern limb of the syncline (Nos. 96, 98a, 98c, 99a–b, 100b). All these rocks are very similar to one another, but nevertheless, according to certain features of structure and mineralogical composition, they naturally divide into three groups. The first includes dense, amygdaloidal rocks, often with porphyritic structure, rich in glass. Sometimes the amygdules reach very considerable sizes (more than 10 cm) and are filled with agate, zeolites, or quartz, usually accompanied by silicification of the nearest part of the effusive rock. Small amygdules possess a regular ellipsoidal, often almost spherical, form and are filled with a brown siliceous substance—tachylite². Rocks with a strongly developed amygdaloidal structure do not have a porphyritic structure. The latter is more sharply manifested in specimens devoid of amygdules or containing them in very limited quantity (see the table). The amount of glass varies somewhat, but always amounts to approximately half of the rock. In the upper porous rocks it is developed much more strongly than in the porphyritic ones, which is readily explained by the conditions of crystallization. Specimens 98a, 92, 96, and 99a of the table appended here satisfy the characteristics of the rocks of this group.

¹ See the vertical sections of the productive series in the article by M. A. Usov (20).

² I have retained Karpinsky’s name (3, 33) for the aggregate-polarizing, colloidal character of formations that are very widespread in these rocks.

COMPARATIVE TABLE
of the principal features of the alkaline basalts of Kuzbass.

No. of specimen	Geographical position of occurrence	Rock coloring	Structure	Grain size in mm: Fedorov	Grain size in mm: main mass	Main constituents	Structure of the groundmass
98 a	Saltymaksovsky ridge, zaimka Yokina.	Grayish-green on the surface and gray-black in fracture.	Fine-grained, augite-bearing.	—	0.35 to 0.014	Plagioclase, tachylite, glassy pyroxene.	Hyalopilitic.
92	Babii Kamen’, Silno-chernaya.	Dense, with a very pronounced porphyritic character.	—	0.57–0.35	0.21 to 0.025	Plagioclase, glass, tachylite, pyroxene, calcite.	Hyalopilitic.
96	Saltymaksovsky ridge, winter hut “Koryazhnaya.”	Porphyritic, with rare phenocrysts.	—	1.20–0.42	0.19–0.02	Plagioclase, glass, tachylite == pyroxene.	Hyalopilitic, in rare cases approaching intersertal.
99 a	Saltymaksovsky ridge, northern end of the Studenyi forest.	Porphyritic, with a dense glassy groundmass.	—	0.87–0.17	0.24–0.07	Plagioclase, glass, pyroxene, tachylite, amphibole, colloids.	As in the preceding.
98 c	Same, where 98 a.	Weakly porphyritic and microlitic structure.	—	0.7–0.24	0.14–0.03	Plagioclase, pyroxene, glass—tachylite and calcite.	Transitional from hyalopilitic to intersertal.
99 b	Together with 99 a.	Almost even-grained.	—	—	0.7–0.1; mean value 0.25	Plagioclase, glass, pyroxene, tachylite, etc.; amphibole, colloids.	Transitional from intersertal to ophitic.
100 b	300 meters north of 99 a.	Sharp porphyritic and weak amygdaloidal structures.	—	5.7	0.7–0.05	Plagioclase, pyroxene, tachylite, colloids, cement and much glass.	Transitional from intersertal to ophitic.

Rocks of the second group are characterized by weakly expressed porphyritic and amygdaloidal structures, up to their complete disappearance. Usually these rocks are recrystallized much more strongly than the rocks of the first group, which is in complete harmony with the character of the structure of the groundmass. In the rocks of the first group the groundmass has a hyalopilitic structure, but as the amount of glass decreases the structure approaches intersertal. Rocks of the second group always have a groundmass structure transitional in character from hyalopilitic to intersertal. The relative poverty in glass and the absence of a porphyritic structure allow these rocks to be regarded as the inner parts of flows, where conditions for crystallization were most favorable. This includes samples 98c and 99b of the comparative table.

Rock No. 100b occupies a somewhat separate position (see table). The combination of a sharply expressed porphyritic structure with an almost complete absence of glass does not allow it to be placed within the rocks of either the first or the second group. The size of the phenocrysts reaches 6 mm, and the crystals of the groundmass are equal in size to the porphyritic segregations of the rocks of the first group. The negligible content of glass in the groundmass, as well as the character of the relations between pyroxene and plagioclase (Fig. 27), create a structure of an intermediate type between ophitic and intersertal. An essential difference from ophitic structure is, as can be seen from the figure, the earlier separation of pyroxene than of plagioclase. Very widespread is the reticulate intergrowth of plagioclases (Fig. 28), both in the porphyritic segregations and in the groundmass. This character of the association of plagioclases is also observed in other basalt samples, but in the present rock it is very sharply expressed, and owing chiefly to it the structure of the groundmass has an ophitic character. A sample of this rock was taken from the deluvium of conglomeratic sandstones underlying the effusive rocks. In the opinion of Prof. M. A. Usov (20, 110), a vein origin of this rock may be assumed.

The jointing of the basalts is very varied. The lava surface is usually irregular. The primary horizontal jointing has almost not changed its original position, although it too is uneven, depending on the irregularity of the soil. The upper part of the flows often acquires an irregular fine prismatic jointing, which in the deeper parts of the flows becomes hexagonal and at times is so well expressed that, for example opposite the Bulanikh River, it gives a splendid example of a giants’ causeway. In some places fan-shaped prismatic jointing is encountered. It is interesting to note the coarse irregular jointing in the rocks of Babiy Kamen and the blocky jointing, recalling the surface of ore stocks, in the anamesitic basalt of the type of the second group (No. 98b). Jointing of the latter character is combined with prismatic jointing and, probably, in contrast to the former, is associated with the inner parts of the flows.

As regards the mineralogical composition, it is rather constant for the rocks in question. The difference consists chiefly in the degree of recrystallization of the rocks, whereby, naturally, part of the minerals is concealed in the glassy groundmass, which is difficult to study. As a result of the study of thin sections of the rocks listed in the table, the following minerals were observed: plagioclase, pyroxene, glass, tachylite, ilmenite, amphibole, calcite, and pyrites¹.

Plagioclase is the most essential constituent of the basalts (Table VIII). In the glassy varieties it is almost the only mineral, if pyroxene, which in these cases plays the role of an impurity, is not counted. In the porphyritic segregations, apart from plagioclase, no other minerals were observed. It is interesting to note that in some samples of both the first,

both of the second group (98-a and 98-c), one can observe, as it were, three generations of crystals. The largest are usually less elongated—short-prismatic; the medium ones crystallize as long laths; and the smallest in size constitute a felt-like mixture (98-a) with the glass and create a picture of a typical hyalopilitic structure, or, in combination with ilmenite flames (98-c), represent a transitional structure from hyalopilitic to intersertal (Fig. 29).

Table VIII.

Sample No.	BNg.	BNm.	BNp.	Plane of intergrowth	2V.	Plagioclase No.	Twin law and features of the crystal
98-a	74°	41°	54°	(010)	—	56	$\dfrac{\perp[001]}{(010)}$. Phenocrystal, length 0.25 mm.
»	34°	—	—	—	—	55	Cleavage on (010) in the same crystal.
92	74°	43°	51°	(010)	+79° +81°	54	$\dfrac{-[001]}{(010)}$. Thin-zoned crystal, length 0.35 mm.
96	60°	72°	38°	(010)	—	60	[001]. Phenocrystal—0.7 mm, zoned, central part.
»	37°	—	—	—	—	60	Plane of intergrowth on (010) in the preceding crystal.
99-a	75°	45°	49°	(010)	+80°	52	$\dfrac{\perp[001]}{(010)}$. Phenocrystal, length 0.35 mm.
98-c	33.5°	61°	75°	(010)	+80°	54	$\perp(010)$. Small phenocrystal—triplet. Combination B₁ B₂.
»	62°	62.5°	41°	»	—	54	[001]. Same. Combination B₂ B₃.
»	73°	41°	53°	»	—	55	$\dfrac{\perp[001]}{(010)}$. Same. Combination B₁B₃.
»	36°	60°	73°	—	—	57	Cleavage on (010) in the preceding.
»	34.5°	—	—	—	—	54	Cleavage on (010). Small phenocrystal.
»	—	45°	—	—	—	53	Cleavage on (0?1). The same crystal.
»	78°	—	—	—	—	55	Cleavage on (110) in the same crystal.
99-b	76°	44°	49°	(010)	+76°	52	$\dfrac{\perp[001]}{(110)}$. Thin lath, length 0.25 mm.
»	61.5°	54.5°	49°	(010)	+78°	48¹)	[001]. Crystal somewhat larger than the preceding one.
100-b	77°	40°	54°	(010)	+76°	57	$\dfrac{\perp[001]}{(010)}$. Very large, 5.7 mm long, phenocrystal. Triplet. Combination B₁ B₂²).
»	32°	61.5°	76°	(010)	—	51	$\perp(010)$. Same. Combination B₂ B₃.
»	63.5°	63°	39°	(010)	—	55	[001]. Same. Combination B₁ B₃. Cleavage on (001) in individual II of the same crystal.
»	—	49°	—	—	—	56	Cleavage on (001) in individual III of the same crystal.
»	—	13°	—	—	—	52	[001]. Lath, length 0.28 mm, in the groundmass.
»	61.5°	63.5°	40.5°	(010)	+76°	55	Plane of intergrowth on (010) in the preceding crystal.
»	35°	60°	74°	—	—	55	Plane of intergrowth on (010) in the preceding crystal.

¹) The point deviates rather strongly from the curve of the Karlsbad law on the twin diagram (30).

²) See Fig. 30.

Taking into account the errors in the determinations, the composition of the plagioclase may be considered almost constant in all groups of rocks. Even for the porphyritic segregations and the main mass (100-b) of one and the same rock it remains constant. Therefore one must think that the three generations of plagioclases described above apparently mark only the moments of origination of new centers of crystallization, without any change in the composition of the liquid phase. With respect to the order of separation of plagioclase, it is interesting to note the following circumstance. From consideration of Fig. 27 one may conclude that we are dealing with the corrosion of augite crystals by later-separating plagioclase laths. Figs. 28 and 31 indicate, if not a later formation of augite, then in any case the simultaneous crystallization of these minerals. Taking into account the increase in the amount of pyroxene in connection with a decrease of glass in the rock, one must suppose that crystallization of plagioclase began earlier than that of pyroxene and may have ended even after the separation of the latter had ceased.

Pyroxene is usually gray; only very rarely, and only in the coarsest-grained varieties, is a faint violet coloration noticeable in it. The mineral extinguishes in patches, which is probably connected with a heterogeneous structure. Sometimes it is zonal, with strong dispersion. The angle of the optical axes is very constant and varies within the limits from \(+58^\circ\) to \(+62^\circ\). The extinction angle varies very strongly, from \(24^\circ\) to \(48^\circ\). This latter circumstance is probably connected with a change in the content of Al, Ti, and Fe (25, 515).

Glass in rocks of the first group reaches 50% of the composition and almost entirely disappears in rocks of the third group. In the first case it is black in color, rarely with feathery, entangled microlites (Fig. 32); in the second it is gray, almost colorless. One must suppose that its coloration is connected with the content of iron and that, probably, in the latter case it represents the most acid part of the magmatic solution, freed from ore and iron-bearing aluminosilicates. It is interesting to note that the appearance of light-colored glass is always associated with a high content of ilmenite, which does not appear in varieties rich in glass.^1)

A very important role in our rocks is played by a brown, often aggregately polarizing substance, to which Karpinsky gave the name tachylite (3, 33). For convenience we retain this name for it in the present description. Tachylite is observed in all basalt samples, and it is difficult to say where there is more of it—in glassy rocks or in well-crystallized ones. In rock 98a, rich in glass, tachylite is developed in a smaller amount than in rock 98c, comparatively poor in glass. In rock 100v the glass is almost absent, but tachylite is present—and in very large amount. One may think that the greater or lesser quantity of this mineral in the rock is determined by its primary composition; this proposition is partly confirmed by the preferential development of tachylite in rocks 98a and 98c of the Lagodkhin occurrence. These rocks characterize different horizons of a sharply amygdaloidal cover. 98a represents the upper, and 98c a part of the cover somewhat removed from the surface. A closer examination indicates an essential difference in the form of manifestation of tachylite in connection with these rocks. In rock 98a it occupies thin ellipsoidal or almost spherical pores (Figs. 33 and 34). Under the microscope one may also observe polygonal formations with a concentric shell-like structure^2) (Figs. 35 and 36). Usually these formations consist of two parts: an outer layer a, representing a radial-fibrous aggregate of thin hair-like individuals, and

^1) The same relation of glass and iron-bearing minerals was noted by V. A. Obruchev for the basalts of northwestern Transbaikalia (31, 445).

^2) According to B. Popov’s terminology (32, 21–23), our spherulites belong to the type of karyogenic ones—those that grow during their formation from the periphery toward the center.

the inner nucleus—b, representing a dark-brown, almost homogeneous mass with threads penetrating into it from a, bundles of hairlike aggregates. In some cases the outer border is developed more strongly than the inner nucleus (Figs. 33 and 35), and sometimes, conversely (Figs. 34 and 36). A weak outer border is usually characteristic of large formations. Very often one may encounter brown, irregularly shaped lumps of tachylite, which in their properties approach the nucleus without any traces of the usual outer shell. In one case it was possible to observe fragments of the crust a in the mass of composition b (Figs. 37 and 38). This phenomenon definitely indicates that, at the moment of filling with substance b, the previously formed crust a, contracting in volume, broke up into small pieces, which were cemented by subsequent portions of the solidifying material. If one takes into account that both varieties of this colloidal substance possess birefringence, partly of an aggregational character (a), partly, probably, from tension (b), then it is not difficult to be convinced that in the present case we are dealing with hydrogels (41, 422), which, depending on the physicochemical environment¹, solidify with one or another water content.

In rock 98-c tachylite never properly fills bounded cavities. In the present case we are dealing only with a substance of type a, of radial-rayed structure, and forming vacuole-like cavities of bizarre shape (Fig. 39). In some cases a concentric structure can also be observed here, but the inner layer, in its external appearance, differs in no way from the peripheral fringe and, like the latter, represents a radial-rayed aggregate. Thus, the tachylite of the deeper parts of the cover is, in its properties, a substance close to the outer crust a of the tachylite that fills amygdules in rocks of the lava surface. In addition, one cannot fail to note still another modification of tachylite, observed, incidentally, only in association with porphyritic segregations of plagioclase. The interval between ophitically arranged plagioclase prisms is occupied by a large aggregate of tachylite (Fig. 40), in which one can clearly notice spots and bands—areas of a highly polarizing, sharply pleochroic, dark-brown mineral, identical in its properties with iddingsite-montmorillonite. Thus, we have grounds to suppose that iddingsite and tachylite represent one and the same substance, solidified in a colloidal or semicolloidal, and perhaps also crystalline, state, depending on the physicochemical environment.

Levinson-Lessing, in the spherulitic rocks of the Mugodzhary Mountains, described spherulites filled with newly formed material, very reminiscent in shape of tachylite formations. It is interesting that these “pseudospherulites” possess a quite round form in their large varieties, and a pear-shaped or irregular one (23, 132) in the groundmass, thereby strongly resembling our formations. As for material close in composition and physical properties to tachylite, the brown colloidal substance described by Baklund (21) in basalt from the Bolshezemelskaya tundra is quite identical with it. Without naming his hydrogel precisely, Baklund considers it closest to the mineral of the chlorite group, gullite (47, 756), and distinct from palagonite (47, 848), chlorophaeite (47, 798), and nigrescite (47, 797). The minerals listed are very close to one another in physical properties, but differ somewhat in chemical composition (21, 90—92), which served for Baklund as the decisive criterion for identifying his mineral with them. Considering his mineral a hydrogel, Baklund believes (21, 95) “that with true glass it enters, as it were, into antagonism, and perhaps represents in part a product of coagulation at elevated

temperature of the latter does not mix with the glass of the residue, of a liquid magma rich in water vapors.” In another case the author allows the possibility of the formation of this substance at the expense of the magmatic alteration of olivine (21, 96). This latter proposition is favored by the composition of the substance, which, judging from the analyses (21, 93—94), contains a large amount of $Mg$ and $Fe$.

It would seem to us that in the present case there is no need to divide tachylite, according to its origin, into several categories, and that, according to our observations, the following propositions may underlie the genesis of this mineral: 1) the presence of properties characteristic of colloidal formations makes it possible to regard tachylite as a hydrogel; 2) tachylite cannot be a secondary product connected with the infiltration of material from outside after the period of cooling of the rock, but is undoubtedly formed in the final stage of its formation; 3) it must be assumed that the period of its formation is the hydrothermal, zeolitic according to Forti (54, 661), phase of rock formation, possessing a rather extensive temperature interval from $0^\circ$ and, approximately, to $350^\circ$; 4) the varied forms of its manifestation, beginning with iddingsite and ending with an almost amorphous substance filling the inner parts of spherulitic formations, are conditioned by the physico-chemical environment; 5) the chemical composition of the given substance is in direct connection with the composition of the magma and of the mineral being replaced, the pyroxenes, as the least stable components of the rocks, and above all olivine, being replaced most often; this, probably, also explains the identification of iddingsite with it; 6) it is very probable that the listed minerals similar to the formations of Backlund—gullite, palagonite, chlorophaeite, and nigrescite, in dependence on their chemical composition, may prove to be formations of the same order,¹) but unfortunately, in order to establish this circumstance, special investigations of these minerals will be required, which may constitute a special subject and does not enter into the tasks of the present work.

Hornblende was recorded only in rocks 99-a—b, which contain colchedans. It is very possible that this mineral is sometimes concealed in the brown tachylitic substance of the groundmass, but in that case its dimensions are so small that they make it completely impossible to distinguish it from the tachylite, similar to it in color. Amphibole appears in brown, with a reddish tint, irregularly colored, weakly idiomorphic crystals, grouped into a small aggregate accumulation (fig. 41), clearly distinguished by their dimensions from the crystals of the groundmass of the rock. At high magnifications the cause of the heterogeneous coloration of the mineral is easily revealed. First of all, small spots—areas (fig. 42) with brownish-red tones of pleochroism, surrounded by a dark-brown border, are clearly observed amid the principal brownish-yellow background. The composing groundmass of the mineral has lower polarization colors than the spots enclosed in it, and very much resembles iddingsite. Cleavage cracks pass through the whole amphibole crystal, but are sharply manifested only in the inner, highly and vividly polarizing areas. In the iddingsite-like material of the groundmass the cracks become broad, strongly developed, with an intense brown-black coloration, evidently caused by the deposition of a pigmenting ferruginous substance. In places in the rock sharply outlined rhombs are encountered, filled with iddingsite with fragments of hornblende. Measurements of the amphibole gave the following constants: $CNg = 18^\circ$; pleochroism along $Np$—light yellowish-brown, along $Ng$—dark brown with a reddish tint.

Calcite is not observed in all specimens of the collection. A little of it occurs in the rocks of Babberu-Kamni, and only in 98c—the inner parts of the amygdaloidal covers—is it more or less well manifested. Usually

¹) Here, probably, many of the rare minerals of the chlorite group, serpentine, and kaolin will have to be assigned (47, 678—852).

represents irregularly shaped fragments—inclusions, with traces of penetration into them, in certain directions, of a glassy material (Fig. 43). On the other hand, in some cases intergrowths of calcite with tachylite are observed in the form of concentrically alternating layers of these minerals (Fig. 44). And, since tachylite is a mineral connected with the primary composition of the rock, the aggregates of calcite should be regarded as remnants of mechanical inclusions of limestone in the basalts, which seized it during their passage through the Paleozoic formations. It is possible that, according to Daly (45, 414), the alkaline character of the basalts resulted from their assimilation of limestones.

The ore minerals are represented most often by pyrite, but here and there pyrrhotite is also noticeable. They have been encountered only in rocks weakly almond-stone-altered (99a, 99b, and 100b). In addition, one cannot fail to note a mineral occurring here and there in the groundmass, resembling mica, with high polarization—colorless, with low relief. Along the margins it is sometimes surrounded by a brown tachylite-like border. Its small dimensions do not make it possible to determine it more precisely. Its low relief does not fit olivine. Since this mineral has been noticed in rocks rich in ore minerals, its formation might be connected with the deposition of sulfides in the rock (36, 22).

Chemical analysis of the rock gave the following results: SiO₂—51.59%, Al₂O₃—17.29%, Fe₂O₃—5.64%, FeO—6.36%, CaO—7.47%, MgO—4.41%, Na₂O—3.40%, K₂O—1.97%, H₂O—0.53%, loss on ignition—1.83%; the rock symbol according to Levinson-Lessing is \(\dfrac{1.99\,\overline{R}}{1.68\,a}\), which in his chemical classification corresponds to the group of effusive analogues of essexites—melaphyres and andesitobasalts (26). Our rocks come especially close in chemical composition to Daly’s trachydolerites (28, 278), differing from the latter by a somewhat lower content of alkalies¹.

Occurrence in formations of one geological period, the alkaline character and similar mineralogical composition of the alkaline basalts and monzonite-essexites leave no doubt that we are dealing with derivatives of one and the same magma, close in composition to alkaline basalts. In the present case we have a convenient opportunity to verify the propositions we have adopted concerning the processes of differentiation of monzonite-essexite rocks. The analyses of rocks 39c and 99a given in Table IX indicate a striking similarity,

Table IX.

Name of rock	SiO₂	Al₂O₃	Fe₂O₃	FeO	CaO	MgO	Na₂O	K₂O
Monzonite-essexite (39c) . . .	51.10	17.76	5.57	7.53	7.15	3.58	2.14	1.14
Alkaline basalt (99a) . . .	51.59	17.29	5.64	6.36	7.47	4.41	3.40	1.97

which is easily explained by quenching phenomena under the conditions of crystallization of rock 39c, taken at a distance of 17 cm from the contact. But more than that, the small differences in the chemical composition of these rocks deviate in the direction foreseen by the process of differentiation. Rock 39c, according to our propositions, corresponds not to the average composition of the magma, but to the first portions of cooling, other conditions being equal, poor in alkalies, since these latter, owing to crystall-

...of differentiation are localized in the central parts of the body. In our analyses this proposition is brilliantly confirmed; it is not difficult to see that the most important difference in the composition of the rocks being compared is the feldspars.

Devonian effusives.

The Devonian effusives are considerably more varied than the rocks of the productive series. Along the Tom River these rocks always underlie \(D_3^2\) and have been found at the following three points: 1) the “Krasnyi kamen’” rocks, 4.5 km above the mouth of the Bel’su River; 2) Simonov’s zaimka, near the mouth of the Taidon River; and 3) individual outcrops of these rocks occurring near the village of Ubiennaya, upstream and downstream from it along the Tom River.

Most abundantly represented in all three exposures are albitophyres, which, alternating with tuffs, make up a rather thick sequence, reaching, for example, below the village of Ubiennaya, about 100 meters. In the headwaters of the Tom, by the Bel’su River, and also in the exposures of Simonov’s zaimka, the albitophyres and their tuffs, underlying \(D_3^2\), are separated from the latter by conglomerates, the pebbles of which are represented by these same rocks. The series of tuffs and covers of albitophyric rocks of Simonov’s zaimka is cut by numerous veins of porphyrites and melaphyres. In addition, in this same exposure there occur covers of porphyrites and melaphyres; below the Taidon River there is a continuous mass of melaphyre (20, 111), while near the village of Ubiennaya the porphyrites form a laccolith-like body.

1. Albitophyres.

The albitophyres of the above-mentioned exposures have been noted by many persons. The rocks of “Krasnyi kamen’” and Simonov’s zaimka were described in the 1890s by Derzhavin under the name of quartz-free porphyries (9, 308) and red porphyries (8, 98). In 1901 the rocks of Simonov’s zaimka (“Osipovskaya anticline”) were studied by Polenov and identified as orthoclase porphyries (12, 288); it must be supposed that the red phenocrysts of albite were taken for orthoclase. In 1909 this same exposure was examined by Yanishevskii (14, 10), who used the nomenclature of the preceding geologists for identifying the effusives. Outcrops of greenstone-altered albitophyres near the village of Ubiennaya were described by Venyukov (7, 43—46) and named by him quartz porphyrites.^1)

It must be supposed that albitophyres take a significant part in the composition of the Devonian series. Judging by the literature, they are very widespread within the Kuznetsk basin and are everywhere associated with Devonian rocks. The “red cliffs” of the Mrassy River at the ulus of Sosnovskii, described by Shchurovskii (2, 147), Bogdanov (4, 201), and Derzhavin (8, 98), are undoubtedly composed of albitophyres. With these same rocks Derzhavin (6, 98) identifies the red porphyries in outcrops along the Kuznetsk road near the Khomutinnaya River, below the village of Zagornaya. On the V. Ters’ River, in the upper reaches of the B. Abata, Gerngross (1, 333—334) notes “red porphyry,” very similar to the rocks of the Mrassy River; the rocks of these same outcrops are called by Polenov (12, 289—294) orthoclase porphyries. Finally, numerous outcrops of quartz and quartz-free porphyries are described by Tolmachev (13, 524—533). Many varieties of these rocks, especially their keratophyric varieties, come very close to our albitophyres.^2)

^1) It is interesting to note that on the Kungurka River (7, 95) Venyukov discovered a conglomerate with pebbles of these rocks.

^2) Especially close here are: the group of quartz porphyries “associated with diabase rocks” (13, 527), and quartz-free porphyries associated with porphyrites (13, 530).

In the rocks of “Krasnyi Kamen’” and in the outcrops of Simonova Zaimka, rocks of this type are ash-gray, dense varieties, with a usually weakly manifested porphyritic structure and an aphanitic groundmass. Amygdaloidal structure is very widespread. Extremely rarely, and only among specimens from Simonova Zaimka, varieties with a large number of porphyritic segregations of albite are encountered. Quartz segregations were not observed in the available specimens. The rocks are so dense that at times macroscopically they are entirely indistinguishable from tuffs.

Under the microscope one can observe a certain seriality of the porphyritic segregations of albite (Table X), whose sizes range from 1 mm to 0.37 mm. The groundmass consists of a microfelsitic mixture of quartz and feldspar. Sometimes the feldspar of the groundmass appears as long flakes (length—0.08 mm), flowing fluidally around the phenocrysts of albite, and thus the structure approaches trachytic. The groundmass is almost always clogged with a large quantity of iron oxides with an admixture of amorphous clayey material. This material sometimes entirely replaces the groundmass of the rock and is distributed along the cleavage cracks of the albite porphyritic segregations. In places one can observe veinlets of secondary quartz and epidote. No dark-colored component was observed, but it is possible that its absence is explained by complete replacement of the mineral by ferruginous-clayey substance.

Table X.

Specimen no.	BNg	BNm	BNp	2V	Plane of intergrowth	Plag. no.	Twin law and character of the rock
59	77°	16.5°	80.5°	+84°	(010)	7	[001] Pebble of conglomerate of the Bel’sy River
»	73°	25°	70.5°	+78°	(010)	3	— ⟂ [100]/(010). Same rock
60-в	76°	15°	88	—	(010)	4	[001]. Albitophyre from the Bel’sy River
»	74°	17°	84°	±79°	(010)	5	[001]. Albitophyre from the Bel’sy River

Since these rocks were subjected to strong diagenetic processes and did not undergo greenschist alteration, they may quite justifiably be called Lenne porphyries and quartz lanporphyries, in the sense of Prof. M. A. Usov.

The albitophyres in the outcrops of the village of Ubiennaya look somewhat different. Here they are very schistose grayish-green rocks of porphyritic structure. Amygdules filled with calcite are observed. The porphyritic segregations are macroscopically poorly visible, and only under the microscope is albite revealed in a comparatively larger amount than in the preceding rocks, sharply serial, in elongated prisms. The length of the prisms ranges from 1.5 mm to 0.60 mm. The groundmass is of trachytic structure, with a tendency toward fluidal. It consists predominantly of thin laths of albite, not exceeding 0.08 mm in size, a large quantity of titanite, and chlorite-serpentine substance, which finely impregnates the entire rock. In some hand specimens a finely devitrified microfelsitic quartz-feldspar base is well manifested. Sericite is occasionally noticeable in the plagioclases. At times one can observe that the central parts of the plagioclases are replaced by calcite and chlorite-serpentine substance, evidently being the product of

changes of some glassy groundmass. It is interesting to note very original spherulite-type formations observed in one case in a rock with a weakly expressed porphyritic structure. These formations are most often of a regular spherical form, but irregular pear-shaped formations also occur. Usually they consist of an outer quartz shell (Fig. 45) and an inner core filled with a bright-green chloritic substance; sometimes the quartz shell is absent¹.

Macroscopically the rocks are completely indistinguishable from their tuffs. Under the microscope the latter appear as breccia-like formations consisting of fragments of albitophyre with a micro-felsitic groundmass. The cementing substance is a closely intergrown aggregate of calcite, serpentine, and epidote. The rocks are strongly altered and have undergone greenstone alteration. Of all the mineral components of the rocks, only albite is primary (Table XI), at times strongly crushed. Therefore, in contrast to the lenneporphyres and lampophyres, these formations may be called quartz keratophyres, representing the greenstone facies of the preceding rocks (36, 26).

Closely adjoining the quartz keratophyres is a rock (No. 162) composing a dike in the roof of diabase laccolith, which is exposed on the headland along the Tom River, above the village of Ubiënnaya. This light-green, dense feldspathic rock, with a weak porphyritic structure, consists of albite (Table XI) in porphyritic segregations and of a mixture of albite and quartz in the groundmass, finely and weakly impregnated with chloritic substance. The structure of the groundmass is microfelsitic. The size of the porphyritic segregations is from 1.1 mm to 0.67 mm, and in the groundmass—0.01 mm and less. The quartz is very cloudy, the feldspar crushed. In mineral composition and structure the rock is completely identical with the albitophyres of the Bel’sa River and of Simonova Zaimka.

Table XI.

No. of sample	BNg.	BNm.	BNp.	2V	Plane of intergrowth	No. of twins	Twinning law and character of the rock
164b	73.5°	16.5°	89°	+78°	(010)	2	[001] } Quartz keratophyres of the cover of the Tom River, below the village of Ubiënnaya.
”	77°	14°	84°	—	(010)	5	[001] } Quartz keratophyres of the cover of the Tom River, below the village of Ubiënnaya.
167	87.5°	16°	74°	—	(010)	0	[001] } Quartz keratophyres of the cover of the Tom River, below the village of Ubiënnaya.
162	85°	69°	21°	±81°; +81°	(001)	2	[010] (001) — Quartz keratophyre of a dike on a headland of the Tom River, above the village of Ubiënnaya.
”	73.5°	18°	85°	+81°; −83°	(010)	3	[001]. The same rock.
”	17°	73°	88°	—	—	2	Cleavage along (010) in the preceding crystal.

2. Porphyrites.

Rocks of this type are very well represented in the exposures of Simonova Zaimka. In Yanishhevskii (14, 10) the rocks of this exposure are called porphyrites, and sometimes diabase porphyrites (14, 19). In general it must be said that in almost all investigators of Kuzbass, porphyrites, and also the melaphyres and diabases described below, were not separated, and usually under the term diabase or

melaphyres there occurred various rocks both of the productive series (basalts and monzonite-essexites) and of the Devonian sequence (porphyrites, diabases, melaphyres). Therefore literary identification is very difficult, but there is no doubt that the majority of the plagioclase porphyrites described by Tolmachev (13, 611—614), especially their group associated with the Devonian deposits of the rivers Tersa, V. Tersa and Belsy (13, 614), are identical with the rocks described by us.

Porphyrites are represented by amygdaloidal rocks, with a sharply expressed porphyritic structure and very variable in color. The basic tone is gray-black with a weak greenish tint. Sometimes the rocks assume a light-gray color and in this case prove to be almost completely replaced by calcite (No. 110). At times a weak greenish tint is comparatively clearly manifested (No. 111), giving the rock some resemblance to diabases. In both the first and the second case, the changes in coloration coincide with the presence, in the veins, of dislocations of the disjunctive type, most likely contemporaneous with small faults and thrusts in the productive series of the Kuzbass (20, 98—99 and 112).

The mineralogical composition is very simple. The porphyritic segregations are represented in most cases only by plagioclases, varying in grain size usually from 3 mm to 4 mm. The finest-grained variety (No. 109) has phenocrysts varying in size from 0.43 mm to 1.02 mm. The main mass of pilotaxitic structure consists chiefly of thin laths of plagioclase, magnetite, quartz, calcite and chlorite. The size of the plagioclase grains in the groundmass varies from 0.08 mm to 0.03 mm.

The plagioclase of the porphyritic segregations varies in composition from number 41 to 51 (Table XII), so that, taking its composition into account, our rocks could boldly be called labradorite porphyrites. The always sharply zoned crystals are often sericitized and bear traces of deformation, manifested in the bending of the twin seam or in the breaking-up of the crystal (Figs. 46 and 47).

Table XII.

Sample No.	BNg.	BNm.	BNp.	2V.	Extinction plane	Plagioclase No.	Twin law	Features of the crystal and of the rock
109	68°	46°	52°	+80°	(010)	42	[001]	Zoned crystal. Feldspathic porphyrite. Dike 2.25 meters thick. Quartz is abundant.
”	26°	—	—	—	—	43	Plane of intergrowth along (010)	Zoned crystal. Feldspathic porphyrite. Dike 2.25 meters thick. Quartz is abundant.
110	30°	63°	79°	+78°	(010)	48	⟂ (010)	Crystals zoned. Plagioclase porphyrite1. Dike 1 meter thick. Quartz is abundant.
”	65°	52°	49°	+80°; +75°	(010)	46	[001]	Crystals zoned. Plagioclase porphyrite1. Dike 1 meter thick. Quartz is abundant.
”	63.5°	49°	47°	+76°	(010)	48	[001]	Crystals zoned. Plagioclase porphyrite1. Dike 1 meter thick. Quartz is abundant.
111	65°	58°	43.5°	+80°	(010)	51	[001]	Labradorite porphyrite with a very small quantity of quartz.
112	32°	60°	79°	+80	(010)	50	⟂ (010)	Labradorite porphyrite. Quartz absent.
113	71.5°	20.5°	83°	90°	(010)	37	⟂ \(\dfrac{[100]}{(010)}\)	Quartz porphyrite. Very much quartz.
”	71°	20°	83	90°	(010)	37	”	Quartz porphyrite. Very much quartz.

Magnetite appears in these rocks in unusually great abundance and ranks second in amount after plagioclase. With changes in the composition of the rock, the amount of magnetite does not change.

Quartz usually occurs in small quantity, in xenomorphic grains, often with cloudy extinction. Sometimes it is without cloudy extinction; in such cases it may be secondary. A marked decrease in it is observed in connection with an increase in the basicity of the plagioclase, often to the point of complete disappearance (No. 112).

Chlorite occurs in variable quantity. It is probably formed at the expense of the primary dark-colored component. In some hand specimens it is almost absent; in other cases it constitutes a considerable part of the principal mass of the rock.

Calcite is very widespread. It fills amygdules, is deposited along cracks, and in some cases almost completely replaces the rock.

Thus the group of rocks described gives a whole series of transitions from felsitic to labrador porphyrites. But the matter is not limited to this. In the bodies of the rocks described there occur, in the form of vein-like masses, more acidic formations, which may safely be called quartz porphyrites. These rocks most probably represent a natural transition from porphyrites to albitophyres, with which the latter are always associated.

Quartz porphyrite (No. 113) is a rock with a sharply expressed porphyritic structure. As porphyritic segregations there are observed only red oligoclase (Table XII), in long (from 5 mm to 1.50 mm), prismatically elongated crystals. The groundmass is dense, reddish-brown in color, with a faint greenish tint, and consists of star-like arranged laths of plagioclase (Fig. 48), the intervals between which are filled with ore and a light feldspar-quartz aggregate, accompanied by calcite, epidote, sericite (very little), and chlorite, formed most probably at the expense of the primary dark-colored component. Here and there apatite appears in comparatively large quantity. A major peculiarity of this rock is the abundance of magnetite, whose fine dust strongly impregnates the plagioclases; their red coloration is due to the transformation of this mineral, in connection with diagenetic processes, into ocherous clay, visible under the microscope.

To this same group of rocks should be assigned rather well-developed rocks which, in outward appearance, are very similar to the labrador porphyrites described, and which crop out from beneath the conglomerates not far from Simonova Zaimka, near the village of Kalashnikova. These sharply porphyritic formations contain a large number of grayish-green phenocrysts of plagioclase immersed in a grayish-black, weakly greenish groundmass. Here and there, on surfaces of irregular jointing, dirty-green spots of sericite substance may be observed, giving the rock the general appearance of a diabase.

Under the microscope it proves that, besides plagioclase, a brownish-green, iddingsite-like mineral, forming pseudomorphs after some dark-colored component, takes a rather substantial part in the porphyritic segregations. The groundmass is fine-grained, with a hypidiomorphic structure, and consists of plagioclase, magnetite, and a large amount of brown, biotite-like iddingsite with blurred outlines.

The plagioclase of the porphyritic segregations reaches 3.10 mm, is sericitized, and strongly broken by irregular cracks. On its uneven and irregular surface no kaolin coating is visible anywhere. Only here and there are sericite and calcite noticeable in small quantity. The numerous cracks are filled with the same brown, migratory iddingsite. The surface of the mineral during extinction is extremely irregular and recalls coarse perthitization, which causes great difficulty and inaccuracy in measurements on the Fedorov stage. Repeated measurements gave, on the average, the following results:

\(BNg = -74^\circ;\ BN m = 18^\circ;\ BN p = 82^\circ;\ 2V = -88^\circ.\) The plane of intergrowth is \(-(010)\). The axis belt gives No. 36 on the curve according to the complex twinning law \(\frac{[100]}{(010)}\). It is possible that part of the calcium was lost by the plagioclase in the process of alteration of the rock.

The rock described should be called navite (51, 1100), since, in addition to plagioclase, an important role in its composition is played by a secondary iddingsite-like mineral, which is usually considered a replacement product of olivine and on which we deem it necessary to dwell somewhat. In principle this biotite-like mineral differs little from the iddingsite of the monchiquites and essexites, where it more often replaces pyroxene. The whole difference consists in the fact that in the present case its color is somewhat lighter than in those rocks, and there is not observed such a large quantity of brown ferruginous flakes that clog the material and mask its mica-like cleavage and high birefringence. Having agreed to call this mineral iddingsite, we consider it necessary to point out once more that there are absolutely no grounds for monopolizing for olivine the right to be replaced by iddingsite. It must be assumed that this mineral can, with equal success, give pseudomorphs both after olivine and after pyroxene. In our rocks we did not observe fresh, unaltered olivine in a single case. The very composition of the rock—a combination of comparatively acid plagioclase with olivine without any other dark-colored component—is undoubtedly unusual for effusive rocks. It is enough to look at the scheme of effusive rocks proposed by Prof. M. A. Usov (36) to be convinced that rocks of such a type, with the exception of navite, have not yet been encountered. It seems to us that navite itself as well, since in it, judging from Rosenbusch (51, 1100), there is evidently only iddingsite, cannot with full right lay claim to containing olivine, and it is more probable to consider that in rocks of our type iddingsite most often replaces pyroxene. According to Rosenbusch’s definition (50, 159), this mineral¹ is close in chemical composition to serpentine, differing from it by a lower water content and by the presence of iron. Iddings assumes that iddingsite is a variety of serpentine, perhaps antigorite (38, 366), microscopically lamellar and intergrown with hematite.

Since pyroxene often passes into serpentine, one may consider it very probable in the given case that pseudomorphs of iddingsite have formed after pyroxene. As for the conditions under which these changes may take place, it must be supposed that the formation of iddingsite occurs in the hydrothermal phase of the formation of the rock, whereas serpentine² is more often a mineral of diagenesis and greenstone alteration.

3. Melaphyres.

Under this name I have distinguished comparatively fresh basic rocks, occurring together with porphyrites in the Devonian sequence of Simonova Zaimka (20, 11). Usually these are black rocks with platy jointing and a sharply expressed porphyritic structure. The porphyritic segregations are represented by lustrous, almost black crystals of plagioclase and by a small quantity of pyroxene. The groundmass consists of short columnar plagioclase microlites, up to \(0.1\) mm long, immersed in a fine-grained mixture of magnetite and chlorite-serpentine, possibly formed at the expense of a primary glassy base. Sharply bounded areas from the rest of the mass are observed

rocks separate portions of the ophitic structure, and then the size of the plagioclase prisms reaches 0.40 mm. In this case the porphyritic segregations disappear. As secondary minerals there are observed iddingsite, serpentine, and calcite.

The plagioclase is zonal, with numerous inclusions of magnetite, often densely arranged along individual zones of the crystal. Probably the black coloration of the feldspar is directly dependent on the quantity of inclusions of this mineral. No alteration into sericite is observed, and the surface of the plagioclase crystals is entirely clean, devoid of a clayey coating. It is interesting to note the somewhat original structure of one zonal crystal (Fig. 53). The central part of the prism consists of two capriciously intergrown individuals, a and b, optically oriented independently, but differing in composition and not forming a twinned intergrowth (Table XIII). Measurement of \(2v\)¹) gives for a—\(87^\circ\) and for b—\(+81^\circ\). According to determinations of the plagioclases of this rock, plagioclase No. 77 may be assigned to a, and No. 61 to b. Most probably, in the present case we are dealing with incomplete diffusion of the substance of a and b at the moment of crystallization. In some cases, especially near portions of the ophitic structure, the porphyritic segregations of plagioclase undergo replacement, at times entirely, by iddingsite or chlorite-serpentine. Sometimes the central part of such pseudomorphs contains low-polarizing aggregates with coarse polysynthetic twins—possibly zeolites²).

Table XIII.

No. of specimen	BNc.	BNm.	BNr.	2V.	Pl. intergrowth	No. plag.	Twinning law and features of the crystal
114	38°	60°	70°	+81° +81°	(010)	61	\(\perp (010)\) part b of a zonal crystal (Fig. No. 52).
»	54°	87°	36°	−86°	(010)	77	[001]. \(B_1\)—n. Sharply zonal triplet.
»	69°	28°	73°	−84°	(010)	80	\(\dfrac{\perp [001]}{(010)}\). In I—III
»	45°	60°	60°	−85°	(010)	77	\(\perp (010)\). In II—III.
»	58°	74°	37°	+80°	(010)	63	Very small, crystal close to the groundmass.
116	45°	62°	57°	−80° −80°	(010)	80	\(\perp (010)\) Inner part of a sharply zonal crystal.
»	56°	86.5°	34.5°	—	(010)	75	[001]. Outer part of a small crystal.
»	51.5°	88°	35.5°	—	(010)	78	[001]. Inner part of the preceding crystal.
»	58.5°	75°	34°	+88° +87°	(010)	67	[001]. Plagioclase of a portion of the ophitic structure.

Pyroxene occurs in large, rare plates with a distinctly visible, often fine, diallage-like parting; it is gray, without pleochroism. \(2v = +60^\circ\); \(CNg = 39^\circ\). In the groundmass it is almost entirely replaced by a greenish-brown serpentine-chlorite substance.

¹) In both cases exits of both optical axes were observed.

²) Cf. the phenomenon of autometasomatism in monchiquite-essexites.

A very large role in the rock is played by a secondary mineral—iddingsite—pleochroic in brown tones, with mica-like cleavage and straight extinction along it. In some cases it very well preserves the properties described, but at times it passes noticeably into serpentine—chlorite. In this case a fibrous structure characteristic of serpentine begins to predominate in the coloration. It is curious that this process is sharply manifested in a somewhat crushed rock (No. 116). It must be thought that in the present case we are dealing with a process of diagenesis of the rock. Iddingsite is rarely observed in the main mass of the rock, where chlorite-serpentine material predominates. Usually it fills cracks in the feldspars, sometimes replaces them entirely, but apparently most often forms pseudomorphs after the primary dark-colored component of the rock, perhaps even after olivine¹. Sometimes replacement of iddingsite and serpentine by calcite may be observed (fig. 54), probably in the process of later diagenetic changes of the rock.

In their freshness the rocks differ sharply from the porphyrites described, together with which they occur. Nor do they resemble the trachybasalts of the Saltymakovo Range and the Karakan Mountains. In the present case we are dealing with diagenetically altered rocks, apparently with a lower alkali content, judging by the more basic plagioclase and the magnetite replacing here the ilmenite of alkaline basalts. It is quite possible that the melaphyres represent only the best-preserved basic varieties of the porphyrites described².

4. Diabases.

These rocks compose a laccolith-like body (20,122) on the right bank of the Tom River, somewhat above the village of Ubiennaya—halfway between it and the village of Pachinskoe. It is possible that the laccolith discovered by Venkov on the left bank of the Tom River, 1–2 kilometers southeast of the village of Mitrofanova, constitutes one and the same body as ours. According to Venkov’s description, his laccolith is cut by a vein of quartz porphyrite and is elongated from NE to SW, so that the strike of its long axis corresponds exactly to the course of the river³ from our outcrop to the village of Mitrofanova (7,54–55). The similarity is completed by the close mineralogical composition and by a vein of albitophyre lying near our body (20.123).

The diabases are grayish-green massive rocks varying in structure. The rock taken 10 meters from the contact has a weak porphyritic structure. The mineral of the porphyritic segregations has not been preserved; in its place we have aggregates of secondary formations, chiefly sericite. Most probably it was plagioclase. The groundmass possesses a residual primary ophitic structure and consists of serpentine and sericite, in a felt of which fragments of plagioclase prisms up to 0.58 mm long are noticeable. More massive portions of this rock, situated farther from the contact of the body, indicate a transitional structure from hypidiomorphic to gabbroic and vary in grain size from 0.5 mm to 2.5 mm. The chief components are plagioclase and augite, to which secondary minerals are admixed in large quantity: serpentine, titanite, zoisite, calcite, and a little sericite.

Plagioclase in areas of gabbroid structure does not have rectilinear boundaries and is closely intergrown with pyroxene. In the less coarse-grained varieties it appears as short-columnar prisms growing into the body of xenomorphic pyroxene, and thus represents an example of a poikilo-ophitic structure (Fig. 49). Usually the plagioclase is strongly altered, which greatly hinders its determination. A small, rather well-preserved grain was measured: \(BNg = 77^\circ\), \(BNm = 13^\circ\), \(BNp = 89^\circ\). Plane of intergrowth \((010)\); No. 30 according to \(\frac{1}{(010)}[100]^{1})\). The mineral more often passes into zoisite. Sericite is observed very rarely.

Pyroxene is an ordinary, weakly violet augite with noticeable diallagic parting. In the coarse-grained varieties it has rectilinear boundaries, sometimes very well expressed. It often passes into serpentine (Figs. 50 and 51). Serpentine is manifested in these rocks in a very peculiar way. In the marginal facies it alone replaces all the femic components of the rock and is always accompanied by a large amount of titanite. In the coarser-grained varieties of the central parts of the laccolith there is less serpentine, but augite also appears, often clearly passing into it. In such cases serpentine fills the rectilinearly bounded areas characteristic of pyroxene (Fig. 51), in the center of which there is always a certain number of titanite crystals, thus marking the composition of the primary mineral. Sometimes, evidently in the subsequent stages of alteration of the rock, serpentine is replaced by calcite, and we have spindle-shaped sphene crystals in aggregates of calcite (Fig. 52).

The rock is undoubtedly very close in composition to the more basic varieties of porphyrites.

CONCLUSION.

The igneous rocks of the area studied naturally fall into two groups: the magmatic rocks of the productive series of the Kuzbass and Paleozoic effusives, connected chiefly with the Devonian deposits.

In the first case we are dealing with trachybasalts and their hypabyssal analogues, monzonite-essexites; in the second—with a diverse complex of rocks consisting of albitophyres, porphyrites, diabases, and melaphyres.

The monzonite-essexites are typical hypabyssal rocks, varying strongly in structure and mineralogical composition. The variation in composition is due chiefly to the process of crystallization differentiation and, to a lesser degree, to assimilation of the enclosing rocks. The latter process is felt only over a distance of 17 cm from the direct contact, with a total thickness of the body of 60 meters.

The trachybasalts in the collection are represented exclusively by glassy, often amygdaloidal varieties. Judging from the plagioclase, the rocks are very constant in their chemical composition. Only a certain variability in structure and mineralogical composition is observed in connection with a greater or lesser degree of crystallization. The most glassy varieties have a hyalopilitic structure and a small amount of pyroxene. With the decrease of glass the porphyritic structure appears more distinctly, and the amount of pyroxene and ilmenite increases in the groundmass. The structure of the groundmass in these varieties changes from intersertal to transitional toward ophitic, but always with some amount of glass.

\(^{1})\) Probably here we are dealing with the most acid and therefore well-preserved plagioclase in the rock.

As in the monzonite-essexites, so also in the basalts, pyrite and pyrrhotite are very frequently encountered, marking the last terminal stages of rock formation. To these same final moments of rock formation should be referred the formation, in the monzonite-essexites, of a brown iddingsite-like mineral, forming pseudomorphs after pyroxene and other components of the rock, and, in the trachybasalts, of tachylite. In both cases the substance is capable of migration and fills cleavage cracks, zone boundaries, and sometimes replaces almost entirely the plagioclases, at whose expense it certainly could not have formed. The origin of this material must be assumed to be connected with the final hydrothermal (zeolitic according to F. Vogt) phase of crystallization of the rock.

The albitophyres of the Devonian are represented either by diagenetized rocks approaching leneporphyres and quartz keratophyres, or by quartz keratophyres that have undergone greenschist alteration¹. In the first case they occur in the middle and upper course of the Tom’ River, outside the area of influence of the Tom’ overthrust (20, 119–129); in the second, they are confined to the Devonian sequence that takes part in this large, disjunctive and intense nappe dislocation. In the available collection the albitophyres are represented chiefly by quartz varieties, but, judging from the literature, as well as from individual rarer specimens, their quartz-free varieties, constituting transitional forms to porphyrites, must also exist.

The porphyrites form small veins in the albitophyres, as well as sheets (near the village of Kalashnikova), overlain by Upper Devonian conglomerates. The rocks are very variable in composition and approach the albitophyres in their most acidic varieties—quartz porphyrites. The latter have been found in the form of vein-like masses in bodies of porphyrites and, apparently, represent a product of the crystallizational differentiation of the latter. The most basic variety is navite. The rocks are strongly diagenetized and have undergone weak greenschist alteration in connection with later movements caused by tangential pressure from the side of the Kuznetsk Alatau (20, 112). In the area influenced by the Tom’ overthrust, the analogues of the porphyrites are diabases, close in composition to the most basic navite varieties.

Somewhat apart from the described group of effusives stand the melaphyre rocks, occurring together with the porphyrites in the Devonian of the Simonova zaimka. In comparison with the latter, these rocks are distinguished by greater freshness and a more basic mineralogical composition. Complete diagenesis and the absence of fine elements do not make it possible to identify them with the trachybasalts of the Karakan and Saltymakovo mountains. It may be assumed that these rocks represent the best-preserved basic derivatives of porphyrite magma.

Bibliography

1. Gerngross, 2nd. A brief geognostic survey of the upper workings of the station, in the Altai Mountains.—Gorn. Zhurn., book V, 1835.

2. Shchurovsky, G. Geological journey through the Altai.—Moscow, 1846.

3. Nesterowsky, N. Description géologique de la partie Nord-Est de la chaîne de Salair en Altai, gouvernement du Tomsk.—Annales de la Société Géologique de Belgique. II, 1875.

4. Botyanov, D. P. Geological outline of the south-western part of the Kuznetsk coal basin and the adjacent uplands.—Zap. Min. O-va, XVIII, 1893.

5. Derzhavin, A. Geological observations in the basin of the Tom River.—G. Zh., No. 10, 1893.

6. On-zhe. Preliminary report on geological investigations carried out in the summer of 1893 in Tomsk Governorate.—G. Zh., 1895.

7. Venyukov, P. Geological description of the south-eastern quarter of sheet 14 of row VII of the ten-verst map of Tomsk Governorate (the Bymakhonka sheet).—Tr. Geolog. chasti b. Kabineta, II, 1896.

8. Derzhavin, A. On the Kuznetsk coal basin.—Geologich. issled. po linii Sib. zh. d., I, 1896.

9. Nesterovsky, N. Geognostic sketch of the Kuznetsk coal basin.—Gorn. Zhurn., 1896: III, 243–351; IV, 16–65 and 184–226.

10. Polenov, B. K. Geological description of the north-eastern quarter of sheet 14 of row VIII of the ten-verst map of Tomsk Governorate (the Kolchugino sheet).—Tr. Geolog. chasti b. Kabineta, II, 1897.

11. Nostrandtsev, A. Geological description of the north-western quarter of sheet 14 of row VIII of the ten-verst map of Tomsk Governorate (the Mosty sheet).—Ibid.; II, 1898.

12. Polenov, B. K. Geological description of the north-western quarter of sheet 15 of row VIII and the south-western quarter of sheet 15 of row VIII of the ten-verst map of Tomsk Governorate (the Borisovka and Berezovka sheets).—Ibid.; III, 1901.

13. Tolmachev, I. P. Geological description of the eastern half of the 15th and the south-western quarter of the 16th sheet of row VIII of the ten-verst topographic map of Tomsk Governorate.—Tr. Geol. chasti b. Kabineta, vol. VII, 1909.

14. Yanishevsky, M. Preliminary report on a students’ excursion along the Tom River in 1909.—Izv. Tomskogo Tekhn. In-ta, 24, 1911.

15. Shnel, F. Petrographic study of the diabase outcrops in the environs of the city of Tomsk.—Ibid.; 37, 1915.

16. Yanishevsky, M. Clay slates cropping out near the city of Tomsk.—Tr. Geol. Kom. Vyp., 107, 1915.

17. Butov, P. I., and Yavorsky, V. I. Materials for the geology of the Kuznetsk coal basin.—Mat. po obshch. i prikl. geolog., issue 48, 1922.

18. Yavorsky, V. I. Materials for the geology of the Kuznetsk coal basin.—Mat. po obshch. i prikl. geol., issue 59, 1923.

19. Butov, P. I. Geological sketch of the Kuznetsk Basin.—Collection “Kuznetsk Basin.” Library of the Mining Journal. Publ. “Kuzbasstrest,” 1924.

20. Usov, M. A. Elements of the tectonics of the Kuznetsk coal basin.—Ibid.

21. Baklund, O. O. Basalt from the Bolshezemelskaya tundra.—Tr. Geolog. Muzeya I. P. V. b. Imp. Akad. Nauk, vol. IV, 1910.

22. Gornostaev, N. N. On new laws of feldspar-quartz intergrowths of the graphic type.—Izv. Tom. Tekhn. In-ta, vol. 46, 1924.

23. Eremina, E. V., and Levinson-Lessing, F. Yu. Materials for the petrography of the Mugodzhar Mountains.—Tr. Imp. SPB Obshch. Est., vol. XXXIII, issue 5, 1905.

24. Lavrovsky, A. V. Plagioclase-augite rocks between the Yenisei and the Lena.—Tr. Obshch. Est. pri Kazanskom un-te, vol. XXXIV, 1900.

25. Levinson-Lessing, F. Yu. On melaphyre.—Izv. P. Polit. in-ta, vol. XX, 1913.

26. Levinson-Lessing, F. Yu., and D. S. Belyankin. Petrographic tables.—Petrograd, 1915.

27. Levinson-Lessing, F. Yu. On the chemical composition of the petrographic provinces of Russia.—Izv. Geol. k-ta, 1923; vol. 42, No. 2.

1. On the same. Petrography.—Leningrad, 1925.

2. Meister, A. K. Materials on the petrography of Crimea.—Izv. Geol. K-ta; vol. 27, 1908.

3. Nikitin, V. V. Fedorov’s universal method.—Petrograd, 1923.

4. Obruchev, V. A. Orographic and geological sketch of south-western Transbaikalia. Part I.—Geol. investigations and exploratory work along the Siberian railway line; issue 22. 1914.

5. Popov, B. A new method for the study of spherulitic formations.—Tr. S.-P. Obshch. Est., vol. XXXIII, issue 5, 1905.

6. Svitalskii, N. Monzonites in the Tsipikan River system.—Geol. investigations in the gold-bearing region of Siberia. Lena gold-bearing district; issue IX, 1913.

7. Usov, M. A. Border Dzungaria. Description of rocks. Vol. II, issue 1.—Tomsk, Izv. T. T. I., 1911.

8. On the same. Fedorov’s or universal-optical method for the study of rock-forming minerals, especially feldspars.—Izv. T. T. I.; vol. 28, 1912.

9. On the same. Phases of effusives.—Ibid.; vol. 46, 1924.

10. On the same. Facies and phases of intrusives.—Izv. Sib. Otd. Geol. K-ta; vol. IV, issue 3, 1925.

11. Yakovlev, S. A. Some data on the question of the influence of specific gravity on the differentiation of magma in the Olonets diabases.—Tr. S.-P. Obshch. Est.; vol. XXXIV, issue 1, 1903.

12. Alling, H. L. The Mineralography of The Feldspars, Part II.—The Journ. of Geol., Vol. XXXI, No. 4, 1923.

13. Bain, G. W. Amount of Assimilation by The Sudbury Norite Sheet.—The Journal of Geol., Vol. XXXIII, No. 5, 1925.

14. Boeke, H. E.—Eitel, W. Grundlagen der physikalisch—chemischen Petrographie.—Berlin, 1923.

15. Bowen, N. L. The Reaction Principle in Petrogenesis.—The Journ. of Geol., Vol. XXX, No. 3; 1922.

16. Idem. The Amount of Assimilation by The Sudbury Norite Sheet.—The Journ. of Geol., Vol. XXXIII, No. 8, 1925.

17. Colony, R. I. The Final Consolidation of Igneous Rocks.—The Journ. of Geol., Vol. XXXI, No. 3, 1923.

18. Daly, R. Igneous Rocks and Their Origin.—New York. 1914.

19. U. Grubenmann und Niggli, P. Die Gesteinsmetamorphose.—Berlin, 1924.

20. Hintze, C. Handbuch der Mineralogie, II B.—Leipzig, 1897.

21. Iddings, J. P. Rock Minerals.—New York, 1906.

22. Phemister, T. C. A Criticism of the Application of the Theory of Assimilation to the Sudbury Sheet.—The Journ. of Geol., XXXIII, No. 8, 1925.

23. Rosenbusch, H. Mikroskopische Physiographie der Mineralien und Gesteine. Bd I₂.—Stuttgart, 1905.

24. Idem. Mikroskopische Physiographie der Massigen Gesteine. II₂.—Stgt., 1908.

25. Rosenbusch, H.—Osann. Elemente der Gesteinslehre.—Stgt. 1922.

26. Schwartz, C. M. A sulfide Diabase from Cook County Minnesota.—Econ. Geol., V. XX, 1925.

27. Vogt, J. H. L. The Physical Chemistry of The Crystallization and Magmatic Differentiation of Igneous Rocks.—Journ. of Geol., XXX, No. 8, 1922.

28. Wahl, W. Die Enstatitaugite.—T. M. und P. M. und D. M., XXVI, 1907.

29. Winchell, A. N. Studies in the Pyroxene Group.—The Amer. Journ. of Science; Vol. VI, No. 36, 1923.

30. Idem. Studies in the Feldspar Group.—The Journ. of Geol., XXXIII, No. 7, 1925.

![[A page consisting of nine hand-drawn geological or petrographic schematic figures, numbered 1 through 9, with regions marked by Greek letters such as α, β, δ and patterned hatching. At the bottom margin is a handwritten note: “Lith. O.Z.U. Tomsk. Circulation 500 copies, Okrlit No. 920.” and the date “IV–1926.”]]

Figures 10–19

Figure 10. Visible labels: a, б, c.

Figure 11. Visible labels: pg, il, a.

Figure 12. Visible labels: б, h.

Figure 13. Visible labels: pg, a, ag.

Figure 14. Visible labels: pg, ag, a.

Figure 15. Visible labels: ag, a, б, β.

Figure 16. Visible labels: a, id, ag, β, б.

Figure 17. Visible labels: id, β, б.

Figure 18. Visible labels: pg, il, ca, a.

Figure 19. Visible labels: ca, б, a, pg.

Lith. O.Z.U. Topogr. Map. 300 copies. Completed IV 1926.

17–1926, No. 4.

20

22

21

Vertical axis: percentage composition

Horizontal axis: distance in feet

Visible curve and reference-line labels include: C, Al₂O₃, SiO₂, FeO, MgO, Na₂O, Fe₂O₃, K₂O, TiO₂, CaO, FeS, FeS₂.

23

![Plate 24: chart and petrographic diagrams with labels 25–29. Visible labels include: A, B, C; Al₂O₃, S·O₂, Al₂O₃, FeO, CaO, Na₂O, H₂, MgO·FeO; vertical axis “percentage composition”; horizontal axis “distance in feet.” Lower diagrams are numbered 25, 26, 27, 28, 29 and contain mineral labels such as q, mt, pg, ag, and others.]

Figures 30–38

30 — labels: III, II, I

31 — labels: $\alpha g$, $pg$, $eg$

32

33 — labels: $\alpha$, $\delta$

34 — labels: $\alpha$, $\delta$

35 — labels: $\alpha$, $\delta$

36 — labels: $\alpha$, $\delta$

37 — labels: $\alpha$, $\delta$

38

Lith. O.Z.U., Tomsk. Print run 500 copies. OkrLit No. 920.
Tomsk, VI 1926. [[unclear: initials/signature]]

Figures 39–46

Visible labels within the figures include: pg, il, a, α, cα, δ, S, s.

39
40
41
42
43
44
45
46

Lith. V.Z.U. [[unclear: abbreviated place/name]]. Print run 500. Leningrad, 1926.
Drawn VI-26. L.Ch.

Figures 47–55.
- Figure 47.
- Figure 48.
- Figure 49.
- Figure 50.
- Figure 51.
- Figure 52.
- Figure 53.
- Figure 54.
- Figure 55.

Explanation of the Figures

1. Glass inclusions in plagioclases: a—plagioclase, b—glass.
2. Character of a quartz aggregate in rock 39b.
3. Bay-like inclusions in a quartz aggregate. Very high magnification; a—glass; b—biotite; Q—quartz.
   4 and 5. Examples of deposition of iddingsite in plagioclases. a—iddingsite. Uniformly shaded areas of plagioclase with identical optical orientation.
   6 and 7. Examples of intergrowth zones in pyroxene.
4. Pseudomorph of iddingsite after pyroxene; id—iddingsite; ag—pyroxene; densely shaded areas of iddingsite are marked.
5. Quartz and calcite in a miarolitic cavity; a—quartz, b—calcite.
6. a—iddingsite; b—biotite; c—chlorite.
7. Q—quartz; il—ilmenite; pg—plagioclase.
8. Penetration of quartz by biotite; b—biotite.
9. a—amphibole; ag—pyroxene; pg—plagioclase.
10. a—amphibole; ag—pyroxene; pg—plagioclase.
11. a—amphibole; b—biotite; ag—pyroxene.
12. a—amphibole; b—biotite; ag—pyroxene; id—iddingsite.
13. b—biotite; id—iddingsite.
14. Form of a miarolitic cavity filled with calcite. or—potassium-sodium feldspar; pg—plagioclase; il—ilmenite; ca—calcite.
15. Q—quartz; b—biotite; ca—calcite; or—potassium-sodium feldspar; pg—plagioclase; ag—pyroxene; mg—micropegmatite.
16. Intergrowth of plagioclase with potassium-sodium feldspar; pg—plagioclase; or—potassium-sodium feldspar; id—iddingsite aggregate.
17. Structural relationships of feldspars and pyroxenes; a—amphibole; ag—pyroxene; pg—plagioclase; or—potassium-sodium feldspar.
    23 and 24. Plagioclase, showing variation in the composition of the norites of Solböre in connection with distance from the lying side of the sill.
18. Myrmekite-like outgrowths of quartz in plagioclase; q—quartz.
19. pg—plagioclase; mr—myrmekite. Quartz—Q—and iddingsite—id—fill a miarolitic cavity.
20. pg—plagioclase and ag—pyroxene in a poikilitic association.
21. pg—plagioclase; ag—pyroxene.
22. T—tachylite; pg—plagioclase.
23. Plagioclase triplet. Roman numerals designate optically differently oriented individuals.
24. pg—plagioclase; ag—pyroxene.
25. Microlites in the glass of a paleotypic basalt.
    33, 34, 35, and 36. Tachylite aggregates; a—outer shell of radial-rayed structure; b—inner core, a homogeneous mass.
26. Fragments of the crust a of tachylite in the mass of composition b.
27. Structure of the outer crust of tachylite.
28. a—tachylite; pg—plagioclase; il—ilmenite.
29. id—iddingsite; a and b—outer shell and core of tachylite; pg—plagioclase.
30. a—amphibole; pg—plagioclase.
31. a—the freshest areas of amphibole; b—iddingsite-like material.
32. a—glass; pg—plagioclase; ca—calcite.
33. a—tachylite; ca—calcite.
34. q—quartz; b—chlorite.
    46 and 47. Deformed plagioclase crystals; s—sericite.
35. pg—plagioclase; m—magnetite; a—quartz-feldspar aggregate.
36. ag—pyroxene; pg—plagioclase.
37. ag—pyroxene; a—serpentine.
38. a—serpentine; t—titanite.
39. a—calcite; b—titanite.
40. Zonal prism of plagioclase. The zoning is emphasized by a thin dusting of magnetite. Individuals with identical optical orientation are uniformly shaded.
41. a—calcite; id—iddingsite.
42. a—alkali feldspar; b—micropegmatite.

1. M. A. Usov. Facies of effusives. (36, 7–21). ↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩↩

2. Tolmachev described (13, 5?2–594) augite porphyrites very similar to our melaphyres from the N. Terst River, in whose inclusions Upper Devonian fossils were found. ↩↩↩↩↩

3. See the map accompanying the article by Derzhavin (6). ↩↩