I. I. Ammosov.

Petrographic Study of the Coals of the Bukachacha Deposit of Transbaikalia

INTRODUCTION

Twenty-three samples of Bukachacha coals, sent to me by the East Siberian Geological Trust, were subjected to petrographic study. These samples are not average petrographic specimens, but are small pieces of core or hand specimens selected in production workings. The samples represent various horizons of boreholes 1, 6, 11, 13, and 38, as well as seams worked by mines I bis, II bis, and II Kapitalnaya; in addition, one sample was sent to characterize the seam exposed by prospecting pit No. 2. A more detailed characterization of the places from which the submitted samples were taken is given in Table 1.

The purpose of the present work is a general characterization of the petrographic composition of the Bukachacha coals and the establishment of the most widespread petrographic types comprising these coals. This task is determined both by the poor state of study of the petrographic composition of the Bukachacha coals and by the nature of the samples supplied for investigation. It was mentioned above that the material under study does not consist of specially selected petrographic column samples, but only of small coal hand specimens (10 × 10 cm) taken from various seams. Each such piece represents a coal seam. There is no doubt that it is impossible to characterize an entire coal seam by such small hand specimens.

For compiling a general petrographic characterization, the samples obtained were subjected to the following investigations: a) macroscopic investigation, as a result of which the macroscopic constituent parts of the coal are established; b) microscopic study of the macroscopically identified constituent parts; and c) study of the spore composition of the coals in maceration products. The results of the study of the microflora are set forth in a separate article¹).

The microflora of the Bukachacha coals is represented chiefly by pollen of conifers from the subfamily Abietineae. In addition, pollen of cycads, ferns, and horsetails (?) occurs here. Among the pollen of conifers, pollen of pine, spruce, and an extinct conifer, possibly Pityophyllum, has been established.

I. Microscopic Composition

A. Terminology

In the microscopic study of coals one should distinguish simple and complex petrographic constituent parts. The former are homogeneous and consist of altered cellular tissue of plants. In them either the cellular structure has been well preserved (fusinite), or the cell walls have swollen (semifusinite), or they have completely lost the cellular structure, which, however, is clearly revealed after etching (vitrinite). Conversely, complex microscopic aggregates are not homogeneous, but consist of a transparent (humic) mass and various formed structures, represen—

¹) Ammosov, I. I. Fossil microflora from the Bukachacha coals of Transbaikalia, 1936 (in press).

Table 1

Sampling sites of the Bukachacha coals submitted for investigation.

…by small fragments of altered cellular tissue, spores, indeterminate formations, etc. The terminology of the simple components (fusinite, semifusinite, and vitrinite) requires no explanation, but the terminology of the complex aggregates should be discussed.

The terms clarain (clarite) and durain (durite) were first introduced by M. Stopes to designate macroscopic constituent parts of coal. In this same sense it was recommended that these terms be used by the First International Geological Congress on the study of the stratigraphy of coal-bearing deposits, held on September 9–12, 1935, in Haarlem (Netherlands), at which part of the time was devoted to consideration of the terminology used in coal petrography¹. However, even now the terms durain and clarain are also applied to the naming of microaggregates. In this connection, the principal distinguishing feature of the aggregates mentioned is considered to be the presence of an opaque, cloudy, structureless mass in durite and its absence in clarite. It should be noted, however, that the nature of the opaque mass cannot be regarded as established, and with equal probability it may be assigned both to flakes precipitated from solutions of colloidal humic matter and to fragments of strongly gelified plant tissue of a semifusitic character. The work I have carried out makes it possible to regard the second supposition as the more probable². For example, one may observe that large lenses of semifusinite are accompanied by small structureless fragments, yellowish in polished sections and opaque in thin sections. These fragments are as if split off from the main lens.

semifusinite lying nearby. Then, etching with a mixture of sulfuric and chromic acids reveals a cellular structure not only in the large lenses of semifusinite, but also in the aforementioned small fragments. This makes it possible to regard the fragments of interest to us, previously considered as an unstructured fine-grained opaque humic mass, not as flaky humic formations, but as fragments of semifusinite.

Thus, the difference between durite and clarite, when these terms are incorrectly used to designate microaggregates, is expressed only by the content of formed bodies located within an unstructured humic mass. However, this difference too is completely effaced owing to the presence in coals of a number of such sections and interlayers in which the content of formed bodies will be greater than in typical clarite, but less than in typical durite. Thus, clarite and durite, in the presence of a number of transitional connecting links, have no right to exist as microscopic constituent parts.

Most clarite and all durite consist of fragments of plant tissues, spores, cutinized fibers and cuticles, etc., situated among a transparent (humic) unstructured mass. Thus, these aggregates represent a complex mixture of formed bodies and the unstructured humic mass cementing them. For this reason, the terminology proposed by Thiessen for designating the microcomponents of coal is more suitable than the old terminology of Stopes¹. Thiessen calls attrite (attritus) those portions and interlayers of coal which consist of residual fragments of cellular tissue, other formed elements, and an unstructured mass. I also adopt this term to designate the majority of the microscopic aggregates observed in the coals of Transbaikalia that were studied, but I change its ending to “inite,” in accordance with the international nomenclature adopted at Heerlen, according to which the macroscopic constituent parts of coal are named by various terms but with the common ending “ite” (“en”), and the microscopic ones with “inite.” Thus the term attrinite is used below to designate complex microscopic constituent parts consisting of an unstructured mass and formed bodies. However, the term attrinite embraces a very large group of coals, differing in the degree of saturation with formed bodies, and also in the character of these bodies. Thus, one may observe attrinites containing less than 20% of formed bodies², while on the other hand attrinites occur in which the formed bodies constitute up to 90%. Moreover, different attrinites contain qualitatively different formed bodies. For example, in one attrinite they are represented by small fragments of semifusinite, and in another by spores or cuticle, etc.

All that has been said above compels me to subdivide attrinites according to two criteria, namely: according to the quantitative ratio of the transparent unstructured mass and formed bodies, and, on the other hand, according to the nature of these formed bodies. The second criterion is taken as the basis of the subdivision.

Thus, the following attrinites may be distinguished.

1. Sporinite attrinite, in the composition of whose formed bodies spore exines predominate.

2. Exinite attrinite, where the formed bodies consist of cuticle and spore exines.

Izv. GII vol. 56, issue V. 4.

1. Cutinite attrinite, the shaped formations of which are represented by cuticle.

2. Sporinite-semifusinite attrinite, consisting of spores and small fragments of semifusinite.

3. Cutinite-semifusinite attrinite.

4. Semifusinite attrinite, the shaped formations of which are represented by semifusinite.

In addition, the quantitative ratios of the transparent structureless mass and the shaped formations make it possible to distinguish at least two groups in each of the listed attrinites. Thus, one group of weakly saturated attrinites includes such attrinites in which the content of shaped formations is less than 50%, and another includes those containing more than 50%.

Such terminology embraces the entire diversity of the microstructure and can be successfully applied in the study of diverse coals. However, it does not give a precise indication of the botanical nature of individual ingredients; in most cases, indeed, this will be difficult to establish in strongly altered plant material that has undergone profound transformations in the processes of peat and coal formation. Only in certain fortunate cases, which can be observed in some comparatively weakly coalified coals, is it possible to establish more precisely the original material of the coals being studied. Such portions of coal should, of course, be singled out, naming the components constituting them by special terms, which will make it possible gradually to enrich coal petrography with a number of new ingredients. We already have a case in which one such caustobiolith (lopinite) was distinguished by the Chinese investigator Si 1). He established accumulations of fragments of bark cellular tissue in Chinese coals of Kiangsi province and, after the neighboring city of Loping, named them lopinite. In the coals of the Bukachacha deposit I succeeded in discovering portions consisting of accumulations of needles that had preserved characteristic features of anatomical structure. Such portions are named bukachachinite.

In those cases where an attrinite is composed of plant remains whose botanical nature has been firmly determined, it will be considerably more correct to give it special names (bukachachinite, etc.). Probably in the near future coal petrography will accumulate sufficient material to allow the majority of petrographic ingredients of weakly coalified coals to be linked with their original material. In any case, this is what should be sought in studying the diverse coals of our Union.

B. Microscopic constituent parts of the Bukachacha coals.

In the Bukachacha coals the following simple (indivisible) constituent parts are distinguished under the microscope: the principal humic mass, vitrinite (telinite and collinite), semifusinite, fusinite, exines of macro- and microspores, cuticle fragments, resin bodies, indeterminate oval formations, and mineral impurities. We shall agree to call them components.

Combinations of simple constituent parts give numerous complex microscopic ingredients, hereafter called attrinites.

a. Simple components.

The simple components participating in the composition of the Bukachacha coals may be divided into three groups: to the first group should be assigned the structureless humic mass, vitrinite, semifusinite, and fusinite; to

1) I cite from Yu. A. Zhemchuzhnikov. General doctrine of caustobioliths. 1935, p. 151.

second—spores, cuticles, and resin bodies, and in the third—indeterminate formations. Mineral impurities occupy a special position.

1. Simple components of the first group, formed from the lignin-cellulose tissues of plants

The components included in the first group constitute a single genetic series. It must be assumed that all of them were formed from the cellular tissue of plants, composed of cellulose and lignin, which found itself under different conditions of decomposition.

With more complete biochemical decomposition, leading to the destruction of the cellular tissue, structureless humic substances were formed, the derivatives of which make up the principal structureless humic mass. If the cellular tissue of dead plants entered anaerobic conditions of decomposition but did not undergo such deep decomposition as in the preceding case, then vitrinite was formed from it, still preserving the cellular structure. In the case of preliminary aerobic decomposition and subsequent immersion of the cellular tissue into an anaerobic medium, fusinite was formed. More will be said below about the genesis of these components.

The structureless mass is the chief constituent part of the Bukachachi coals. It is included in the composition of attrinites and here cements various shaped formations (resin, cuticle, indeterminate formations, etc.). In most cases the structureless mass has a homogeneous composition, but sometimes a lumpy composition can be observed in it. Its color changes and depends on the thickness of the thin section, as well as on the degree of “maturity” of the coal. Thus, if one compares thin sections of approximately the same thickness, prepared from the coal of seams No. 0 and No. 1, with thin sections from the coal of all the other seams, the brighter red coloration of the former is clearly noticeable. In all the other thin sections we see a brown, brownish-brown, and brownish-chestnut coloration of the structureless mass. Thus, the color of the structureless mass in the coal of seams No. 0 and No. 1, occurring at a greater stratigraphic depth, is fresher and brighter, with a red tint, whereas in all the other seams it has no red tint, or this tint is very weakly expressed. This undoubtedly depends on the different degree of maturity of the coal, greater in the underlying seams, as should have been expected according to Hilt’s rule.

The color of the structureless mass also changes depending on the thickness of the thin section. Thus, in one thin section, but in portions of it differing in thickness, we can observe transitions from light brown to brownish-brown, brownish-chestnut, and chestnut. However, a change in color caused by an increase in the degree of “maturity” can always be distinguished by the red color, which does not appear in color changes caused by different thickness of the thin section.

The structureless mass must be regarded as the result of a profound alteration of lignin-cellulose plant tissues that were completely destructured, passed into humic acids, and then into their derivatives, which underwent a series of further transformations associated with the different degree of “maturity” of the coals.

Vitrinite occurs in the Bukachachi coals as small interlayers, usually varying in thickness within the limits of 1–4 mm, but occasionally more substantial interlayers of it are encountered, reaching 1 cm. In addition, in thin sections one can observe very thin interlayers of vitrinite, distinguishable only under the microscope.

Interlayers of vitrinite that are macroscopically visible possess features,

are highly characteristic of this component. Thus, their color is black, the fracture is flat-conchoidal, and the luster resinous. It must be noted that the luster of the vitrite of the Bukachacha coals is considerably stronger than the luster of the vitrite interbeds observed by me in the Jurassic coals (conglomerate suite) of the Kuznetsk coal basin, but weaker than the luster of the vitrite of the Lenin coals of Kuzbass, associated with the Kolchugino suite.

This indicates a higher “maturity” of the Bukachacha coals than that of the Jurassic coals of Kuzbass, but a lower one than that of the Lenin coals. In terms of “maturity,” the Bukachacha coals probably stand much closer to the Lenin coals.

In thin sections, the vitrinite of the Bukachacha coals has a reddish-brown coloration (Figure 1). A well-preserved structure of the cellular tissue of plants can often be observed here. It appears sometimes in transverse (Figure 1), sometimes in tangential sections. The magnificent cellular structure of the vitrinite (telinite) of the Bukachacha coals leaves no room for doubt as to its genesis from the cellular tissue of plants (bark and wood). Thus, there can be no question here of the sapropelic-colloidal theory of vitrinite formation. True, the structural areas of telinite are often contiguous with structureless bands of collinite, but this indicates only a deeper destruction of the cellular tissue of plants that has lost its structure here. The formation of vitrinite from the cellular tissue of wood is also confirmed by numerous observations in the Lenin coals of Kuzbass, where the cellular structure of telinite is especially well revealed after etching polished sections, and is also observed in thin sections.

The formation of vitrinite took place under the conditions of a strongly waterlogged peat bog, where decomposition of the cellular tissue of plants occurred, protected by a water cover from the destructive influence of aerobic bacteria. Owing to this, the finest details of the structure of the cellular tissue of wood were preserved in places. Anaerobic bacteria nevertheless exerted a destructive influence on the dead wood and in places transformed it into a structureless state, but toxins, which are products of the vital activity of the anaerobic bacteria themselves, halted their destructive-constructive work at one stage or another, which allowed certain areas of cellular tissue to be preserved.

Fusinite and semifusinite. Large interbeds of fusinite are absent from the studied samples of the Bukachacha coals. Macroscopically, only the thinnest film-like interbeds of hard fusinite can be noticed, occurring sometimes among lustrous coal, sometimes among semi-dull and dull coal.

Under the microscope we see normal fusinite, i.e. opaque, preserving cellular structure and occurring sometimes as rather large, yet still microscopic, interbeds and lenses, clearly distinguished in thin section among the rest of the coal mass (Figure 5), sometimes as small fragments entering into the composition of attrinites. These fragments are usually taken for an opaque humic mass (Figures 2, 3, 6, 9, 10).

Larger areas of fusinite are encountered especially often in interbeds of dull coal, but sometimes it can also be observed in lustrous coal.

Semifusinite, as usual, is in the Bukachacha coals a link joining vitrinite and fusinite into one genetic whole. Between typical semifusinite and vitrinite, on the one hand, and also between semifusinite and fusinite, on the other, there are still intermediate components represented by the cellular tissue of plants altered to a greater or lesser degree. These intermediate components link vitrinite and fusinite into one genetic whole through a series of gradual transitions. In the Bukachacha

In the coals, semifusinite is most often found. It is fairly transparent and has a poorly preserved cellular structure.

There is a considerable amount of semifusinite in the coals studied, but it differs strongly from the semifusinite of Kuzbass coals. Thus, if in the form and size of the lenses, and also in the preservation of the cellular structure, one may draw a parallel between the semifusinite of the Bukachacha coals and the semifusinite of the Prokopievsk coals of Kuzbass, then in transparency it differs sharply from the semifusinite of the Prokopievsk coals. In the Bukachacha coals the semifusinite is considerably more transparent and has a general light-brown color. Usually the coloration of semifusinite is lighter than that of the structureless mass. This is due to the fact that the cells of the cellular tissue in semifusinite have a considerably less dense coloration, approaching light brown with a yellow tint. Therefore the general color of the semifusinite, composed of the color of the substance filling the cell cavities, which, as mentioned, is lighter, and of the color of the substance composing the cell walls, identical with the color of the structureless humic mass, will be less dark than the color of the structureless humic mass. This is clearly seen in Figure 6, where fairly large lenses of semifusinite, still preserving a trace of the original cellular structure, alternate with narrower bands of structureless mass containing yellow spores and small black fragments of semifusinitized tissue. Here we see that the general color of the bands of semifusinite is light brown with a yellow tint, whereas the color of the structureless mass is brown and brownish-brown.

In addition to light-brown bands of semifusinite, preserving remnants of cellular structure and alternating with a brown and brownish-brown structureless mass, in the Bukachacha coals one can also observe original portions of coal consisting of narrow (1–5 µ) structureless bands of brownish or brownish-reddish color, containing no spores. These structureless bands alternate with bands just as narrow (1–6 µ), but lighter in color and also structureless (Figure 9). It must be supposed that we are dealing with alternating bands of various structureless humic mass. However, it is significant that the structureless mass here contains no spores. This indicates the possibility of assuming destruction of the cellular tissue of plants that formed the alternating bands of structureless mass in situ, and this whole complex may be regarded as a modified single plant individual, different portions of whose cellular tissue changed under identical conditions of decomposition but yielded different final products owing to the nonuniformity of the original material. Thus, considering transverse, radial, and tangential sections, for example, of the wood of modern conifers, we may note that the cell walls at the points of contact of neighboring alternating rows form a continuous band consisting of lignin and cellulose. Between these continuous bands of lignin-cellulose composition lie rows of cells consisting of thin cell walls enclosing the internal contents of the cell, the chemical composition of which differs greatly from the chemical composition of the cell walls. The substance filling the cells here decidedly predominates over all the rest. Therefore, during decomposition of the cellular tissue of wood, banded formations will be obtained, as we see in Fig. 9. Let us agree to call such portions, formed during the decomposition of wood, arborinite (arboreus—wood).

Among the numerous theories of the formation of fusite, attention is deserved by the hypothesis of Grand’Eury and Duparque, who relate the formation of fusite to preliminary subaerial decomposition of the cellular tissue of plants in situ, which then passes into anaerobic conditions.

It may be assumed that from identical original material, i.e., the cellular tissue of wood and bark, in one case there may form

vitrinite, which requires for its formation constant anaerobic conditions associated with the immersion of a dead plant in a water-rich peat bog, while in another case fusinite is formed. The presence of the latter in coals, when its content is large, indicates a dry peat bog, or a peat bog with a very unstable water regime, in which prolonged periods of drying were replaced by periods of moistening. Thin interlayers and lenses of fusite, which take only a very small part in the composition of the coal—the main mass of which is composed of vitrinite and shiny striated coal—may form at the expense of parts of plants that protruded above the level of the strongly moistened peat bog and thus, before their immersion, underwent preliminary aerobic decomposition.

If one accepts this conception of the genesis of fusinite and vitrinite, then the formation of semifusinite, which possesses intermediate properties, must be linked with the possible endless diversity in the duration and intensity of aerobic and anaerobic decomposition that the dead cellular tissue may undergo. Thus, the formation of semifusinite occurs at those stages of peat-bog formation, or in those parts of it, where the action of the agents of aerobic decomposition was stronger than in the formation of vitrinite.

Taking into account the possibility of an infinite diversity in the duration and intensity of aerobic and anaerobic decomposition, and their different sequence, we may speak of the presence in coals not only of vitrinite, semifusinite, and fusinite, but in general of a single genetic series—vitrinite–fusinite—between the extreme members of which there are many components formed under intermediate conditions.

I have no doubt also that different cellular tissues participating in the structure of a single plant individual, but performing different functions and often possessing different chemical composition, being now more and now less resistant to bacterial decomposition, will, under identical conditions of decomposition, yield different results. Here we may obtain vitrinite or semifusinite, the genesis of which will be determined not by different conditions of decomposition, but by different initial material. However, such cases will probably prove possible to recognize by the morphological features of the different cellular tissues (cell shape, wall thickness, presence or absence of cutinization), although difficulties may often arise when we cannot give preference to the influence of the initial material or to the conditions of its transformation.

It should also be noted that further changes of the organic substances composing a coal seam take place in the seam, and in this process the substances undergo quantitative and qualitative changes associated with changes in the morphological features of the petrographic constituent parts. This is especially evident when protobitumens (spores, cuticles, resin bodies) are observed in coals at different stages of maturity. Thus, with increasing maturity they change their chemical composition, color, and also the sharpness of their outlines, and gradually merge with the main humic mass, becoming indistinguishable from it.

The members of the genetic series under consideration—vitrinite–fusinite—will likewise gradually change with the change in the degree of maturity of the coals, but the course of these changes has as yet been little studied.

2. Simple components of the second group—protobitumens.

These include resin, cuticles, and spores. All these components possess a yellow and golden-yellow color. They stand out sharply from the brown structureless mass enclosing them.

Resin is encountered chiefly in semilustrous coal, often possessing ocular separateness. It is even possible that there is a genetic connection between ocular separateness and the presence of resin grains occupying central positions in the eyes and causing the appearance here of ocular separateness. However, this supposition requires verification. The ocular separateness of semilustrous coals must be distinguished from the ocular separateness of vitrite, where it has no connection whatever with resin.

The sizes of resin bodies in the Bukachacha coals are very varied. Thus, here we may encounter either fairly large resin bodies reaching a length of 250–500 μ (Figure 4), or considerably smaller ones (see the same Figure 4, and also Figures 7 and 8), when the resin bodies have a length of 5–10 μ. In addition, resin bodies are encountered whose dimensions fluctuate within the indicated limits.

Resin bodies occur in various forms: oval, elongated-lens-shaped, and irregular. In most cases they are somewhat flattened; this must be attributed to the pressure of the overlying sedimentary thickness, which undoubtedly affected the form of the resin bodies. In some thin sections there is observed a lens-shaped, pointed form of resin bodies, having a less bright yellow coloration. Such bodies are usually broken by cracks passing along their long axis. This must be explained by the greater brittleness of the resin bodies than of the humic mass enclosing them. The cracks probably appeared at a later time, when the coal substance, and within it the resin bodies, had been sufficiently strongly diagenized and had become brittle. Only after this did tectonic forces appear, causing the formation of cracks dissecting the resin bodies.

The main mass of the examined samples of Bukachacha coals contains few resin bodies, but interbeds occur that are richly saturated with these formations (Figure 4). Resin bodies occur especially often in semilustrous coals possessing ocular separateness. Sometimes the content of resin bodies in coal interbeds is so great that the latter can undoubtedly be assigned to typical resinous liptobioliths.

The color of the resin bodies varies from pale yellow to bright yellow-golden and even yellow with an orange tint, which depends on the varying thickness of the thin section. We did not succeed in noting a change in the coloration of the resin bodies caused by a change in the “maturity” of the coals, since the difference in the degree of maturity of the upper and lower beds now exposed in the productive sequence of the Bukachacha deposit is probably not great. We mention that the change in coloration of the structureless mass observed in the upper and lower beds is apparently more sensitive than the change in coloration of the resin bodies.

Some resin bodies at high magnifications (up to 2000) have a lumpy and lumpy-cellular structure.

Cuticle often occurs in interbeds of lustrous striated, semilustrous, semidull, and even dull coal. Usually it is thin (1–2 μ), but very rarely thicker cuticle is also encountered, reaching a thickness of 4–5 μ. The color of the cuticle varies from pale yellow to golden-yellow and even orange-yellow. These changes in color also depend on the thickness of the thin section. Smooth cuticle is more often observed, but sometimes dentate cuticle is also encountered.

In the Bukachacha coals one may see both fragments (Figure 4) and an entire closed cuticle (Figures 7, 8, and 10). The latter always outline conifer leaves, which are small in size and therefore entirely

falling within the field of view of the microscope (Figures 7, 8, and 10). This finding is very interesting, since it definitely indicates the formation of certain coal interbeds from conifers.

In addition to the normal yellow cuticle in the Bugachany coals, especially often in vitrinite, one can observe light-brown fibrous formations, strongly resembling cuticle in their form but probably belonging to elements of other plant tissues. Sometimes similar fibers, resembling cuticle, are also found outside vitrinite. Probably these thin strips represent remnants of partitions between rows of wood cells enriched, during the life of the plants, with lignin. This accounts for the relatively slow alteration of such fibers, which is confirmed by their lighter coloration.

Spores. Here we shall mention only observations on spores made in polished sections. The spore composition is described in more detail in a separate article (see above).

The sizes of the spores range from 20–100 μ. Thus, they should be assigned to brev spores¹ (microspores). The usual form of the spores is a lens, in which an internal flattened cavity is quite often visible (Figure 1), but in most cases no internal cavity is visible (Figures 2, 3, and 5).

The color of the spores varies from pale yellow to a rather bright golden-yellow. It is difficult to notice a difference in the color of spores from higher and lower beds. Probably the alteration of their coloration, which in general has already been observed more than once in coals of different degrees of maturity, proceeds more slowly than the alteration of the color of the main humus mass.

3. Simple components of the third group.

This includes only indefinite formations. Indefinite formations occur most often in interbeds of semilustrous and semidull coal. In coal sections (polished sections) perpendicular to the bedding, they have an oval, pith-like, or triangular-rounded shape. Indefinite formations occur either as single specimens (Figure 6) or in groups, in which individual oval bodies closely adjoin one another. It is almost always possible to observe in them a fairly thick rim, amounting to 0.3, 0.25, or 0.15 of the total diameter of these bodies. The sizes of the bodies range from 7 to 250 μ, but bodies of medium size occur more often.

It is clearly noticeable that strings of spores, as well as fragments of semifusinite and fusinite, smoothly bend around these formations, which indicates the considerable strength of the latter. Their rounded-oval form, observed in sections perpendicular to the bedding, also testifies to this. The color of the indefinite formations is brown and brownish-brown, i.e., it coincides with the color of the structureless humus mass. It should be mentioned that the rim of the formations described always has a lighter coloration than the internal cavity.

To clarify the genesis of the indefinite formations, additional studies are necessary. Thus, they may be fungal sclerotia, while some may be pith rays of wood.

Mineral impurities in the polished sections studied occur in small quantities. They are represented by very fine grains

quartz, having an angular-rounded form; in addition, rare grains of sulfides are encountered, and in some polished sections thin clayey interlayers are noticeable. In the maceration products one can observe the above-mentioned grains of quartz and other very fine grains of tabular minerals, the determination of which we were unable to undertake.

6. Complex aggregates.

The simple components described above combine into complex aggregates, called attrinites. An obligatory component in all attrinites is a structureless humic mass. It cements diverse formed bodies. The formed bodies may be represented by one component, for example, spores; by two—spores and resin bodies; by three—spores, resin bodies, fragments of fusinite or semifusinite; by four—spores, resin bodies, fragments of fusinite and cuticle, etc.

Let us agree to call an attrinite consisting of a structureless humic mass and one predominant formed body a two-component attrinite; an attrinite containing two heterogeneous formed bodies—a three-component one, and so on.

In examining attrinites one should take into account the ratio of the structureless mass to the formed bodies. The degree of saturation of the structureless mass with formed bodies is of great importance, since not only the morphological features of the coal depend on it—for example, its luster and dullness—but also its properties (ash content, coking capacity, etc.).

We shall distinguish weakly and strongly saturated attrinites. To the former are assigned attrinites in which the formed bodies make up less than 50% of the total volume of the attrinite, and to the latter—those containing more than 50% formed bodies.

1. Two-component attrinites.

Two-component attrinites proper occur rarely, since, when one formed body decidedly predominates, other components are also found in the same attrinite, playing an entirely subordinate role. We shall agree, however, to call such attrinites two-component; their name will indicate the predominant formed body.

Sporinite attrinite is often encountered in the Bukachacha coals and forms part of bright, semi-bright, semi-dull, and dull coals, where its content varies greatly (figures 3 and 7). It consists of a structureless mass and spores distributed rather uniformly in the structureless mass; not infrequently in this attrinite there are also small fragments of semifusinite, taken by Hoffmann and Stach for an opaque mass which, as they believe, precipitated from a colloidal solution when spores were immersed in it. Thus, according to Hoffmann and Stach, dark areas of opaque mass must always be associated with spores. However, if quite often we do indeed see a connection between spores and areas of “opaque mass,” no less often one can observe its independent position, as well as the absence of “opaque mass” in an attrinite containing spores (figure 3). It is possible that the frequently observed contact between spores and opaque bodies—fragments of semifusinite, in my opinion—should be explained by the forces of adhesion holding these heterogeneous bodies together after they once accidentally came into contact during movements of the plastic humic mass, which already contained

both spores and fragments of cellular tissue which had previously undergone brief aerobic decomposition. The latter ensured the further alteration of the cellular tissue to the state of semifusinite.

The greater part of the spore attrinite of the Bukachacha coals should be assigned to weakly saturated attrinite containing much structureless mass. Only occasionally are small areas of spore attrinite encountered, very rich in spores, which closely adjoin one another.

Cutinitic attrinite is frequently encountered in the Bukachacha coals. It consists of a structureless humic mass, brown, brownish-brown, or reddish-brown in color, and of cuticle. In addition, mineral admixtures and a few resin grains are observed in it, as well as small fragments of black semifusinite. The degree of saturation with cuticle varies. Thus, attrinite containing up to 30 cuticles per 1 mm is encountered—this is strongly saturated attrinite; but it is not uncommon to observe attrinite in which there are only 6–10 cuticles, or even fewer, per 1 mm.

Cutinitic attrinite, whose botanical nature we do not know, should be distinguished from cutinite attrinite, in which it has been possible to establish to what plants and to which of their parts the cuticle belongs.

It was mentioned above that in the Bukachacha coals one can observe a closed cuticle outlining small areas. Within the contour of such a cuticle there is a structureless humic mass and one or two small resin bodies (figures 7, 8, and 10).

As is known, the cuticle covers the leaves and stems of plants with a thin layer and serves to protect them from unfavorable influences of the external environment. Cuticle is also present on the leaves (needles) of conifers. The needle has one additional original feature, namely, it contains small resin canals, the number and arrangement of which play a major role in identifying conifers by their needles¹. The small size of the leaf remains outlined by cuticle (their width ranges from 0.5 to 0.8 mm, and their thickness from 0.05 to 0.07 mm), as well as the presence of resin canals, make it possible to assign these leaves to needles that took part in the formation of the Bukachacha coals. This is also confirmed by the extraordinary abundance of characteristic conifer pollen observed in the maceration products of the Bukachacha coals.

Within the contour of the needles of the Bukachacha coals it is usually possible to observe one resin canal, located near the edge of the needle (figures 7 and 8), but sometimes two such resin canals are also encountered, set far apart from each other. All the remaining space outlined by the cuticle is composed of a humic transparent mass that has not preserved structure and has a brown, brownish-brown, or brownish-reddish color.

The discovery of needle remains in the Bukachacha coals, described here for the first time in coals in general, is of great scientific interest, since it gives, on the one hand, a completely definite indication of the original parent material of these coals, at least of certain interbeds; and on the other hand, the preservation of resin canals in the needles may have great paleobotanical significance, since their number and mutual arrangement will help to establish more precisely the genera of conifers that grew in Jurassic time. In addition, this has purely petrographic significance, making it possible to distinguish a new ingredient with a quite definite petrographic-paleobotanical characteristic.

Let us call this new ingredient Bukachachinite. Bukachachinite occurs rather often in the Bukachacha coals. Thus, I observed it in seam I (from mine II Kapitalnaya), in seam II bis (from borehole 38), and also in seam II (borehole 11 and mine II bis).

The genesis of this cuticular ingredient is sufficiently clear. The leaves of conifers that grew on a peat bog accumulated on the surface of the peat, which had accumulated the dead remains of plants. Here they entered anaerobic conditions, in which the decomposition of the needles took place. In this process the less resistant tissues quickly passed into a structureless humic mass, while the cuticle and resin, which stubbornly resisted decomposition, entered the fossil state after undergoing less profound changes. The wind brought atmospheric dust here, which supplied the finest mineral grains observed between the individual leaves.

It will be of interest to trace the distribution of interbeds of cuticular attrinite throughout the entire thickness of the seam, since this will indicate periods of vigorous leaf fall and, perhaps, will make it possible to calculate the time during which the seam was formed.

Resinite attrinite consists of a structureless humic mass and resin bodies. In addition, fragments of cuticle and spores, as well as small fragments of semifusinite, occur in it (Figure 4). The content of resin bodies is sometimes so great that interbeds of resin attrinite may be assigned to liptobioliths. Resinite attrinite occurs in the Bukachacha coals rather often, but it lies in thin interbeds. This ingredient is especially often observed in coals having lenticular cleavage. Resinite attrinite was formed, probably, under conditions of strong action by biochemical and physicochemical agents, when all the less resistant plant tissues, consisting of lignin and cellulose, underwent deep decomposition, which is associated with the formation of gaseous substances that escaped from the peat deposit; as a result, the residue was enriched with resinous bodies that during the life of the plant had filled its resin canals.

2. Three-component attrinites.

These attrinites consist of a structureless mass and two formal formations participating in the composition of the attrinite in approximately equal measure. Besides them, other formal formations also occur here, but in very small quantity.

Resinite-sporinite attrinite contains spores and resin bodies, which by volume play approximately the same role. This attrinite is very similar to resinite attrinite and, of course, was formed under the same conditions, but during the period of decomposition of organic matter the humic mass was saturated with spores arriving from the atmosphere. The spores sank in the plastic humic mass and mixed with the resin bodies. In the Bukachacha coals this attrinite occurs both strongly and weakly saturated with formal formations.

Sporinite-semifusinite attrinite consists of a structureless humic mass, spores, and an approximately equal quantity of small opaque fragments of semifusinite (Fig. 4); in addition, it sometimes contains a few fragments of cuticle and, more rarely, resin bodies. Like sporinite attrinite, it is formed under conditions of rather strong action by bio- and physicochemical agents, which destroyed the main mass of lignin-cellulose tissues of the plants, which pass into humic acids and then into a humic structureless—

a peat mass. Only from some areas of cellular tissue, which had experienced the alternating action of aerobic and anaerobic factors, fragments of semifusinite were formed, interspersed with spores that were brought here from the air and buried in the plastic humic mass. Sporinite–semifusinite attrinite occurs, strongly and weakly saturated with formed constituents.

3. Four- and five-component attrinites.

Four- and five-component attrinites consist of a structureless humic mass and three or four formed constituents, the contents of which are approximately equal.

Among such attrinites in the Bukachacha coals there occur cutinite–sporinite–semifusinite, sporinite–resinite–semifusinite, etc. Their composition and conditions of formation can easily be inferred from the descriptions given above of the genesis of less complex attrinites.

III. Petrographic types of the Bukachacha coals.

A. Macroscopic characterization.

The main mass of the studied samples of the Bukachacha coals is composed of bright and semi-bright coal. However, on more careful examination of their composition, in some samples it is also possible to distinguish semi-dull and dull interlayers. Of all the samples studied, 17% are represented by bright coal, 46% by semi-bright, 23% by semi-dull, and 14% by dull coal.

In the samples of Bukachacha coals at my disposal, I was unable to observe clearly noticeable lenses or interlayers of fusite. Only along the bedding planes in some samples can one sometimes notice the thinnest films of fusite, which are especially clearly visible in thin sections (Figure 5). Interlayers of vitrite occur somewhat more frequently; these can already be quite readily distinguished even in macroscopic examination, since sometimes they have a sufficiently large thickness—up to 1 cm.

Thus, in the Bukachacha coals one can macroscopically distinguish vitrite, bright streaky coal, semi-bright, semi-dull, and dull coals. Vitrite is a simple constituent, whereas all the others have a complex microscopic composition and have either a homogeneous or a banded texture. Thus, among the complex macroscopic constituents of coals, two large groups can be distinguished by texture—banded and homogeneous. The textural feature should be taken as the basis of petrographic subdivision into major groups, and already within these groups it is necessary to distinguish smaller units, differentiated by luster and brightness¹. Both texture and luster indicate the genetic features of the first stages of coal formation; however, during subsequent transformations of the coal substance, for example with an increase in the degree of “maturity”² of the coal, the textural features will be more po—

constant than luster and brilliance, since the latter changes even with slight nuances in the degree of “maturity.”

The scheme for classifying the macroscopic petrographic constituents of the Bukachacha coals, apart from vitrite and fusite, may be presented as follows.

Table 2 brings together the morphological features of the petrographic constituents of the Bukachacha coals that can be distinguished macroscopically. Homogeneous and banded brilliant interlayers differ in texture, but in the remaining morphological features they are similar to one another. This applies equally to all the other varieties of coal that are identical in luster but differ in texture. Consequently, the characteristics of the homogeneous and banded varieties can be placed in one common table. Some morphological features change gradually from vitrite to dull coal. Thus, the color changes from black to blackish-gray and dark gray, and the luster—from resinous to weak greasy. The structure remains dense in almost all cases¹. Only brilliant coal often has a streaky texture, while vitrite sometimes has a lignitic structure. The parting is predominantly prismatic, but fairly often an eye-like parting is also observed, usually in semibrilliant coal. The fracture changes from flat-conchoidal and streaky, characteristic of vitrite and brilliant coal, to uneven in the other varieties. The listed morphological features are characteristic of humic, weakly coalified hard coals assigned to the gas and long-flame ranks.

Thus, judging by the reflectivity of vitrite, the degree of maturity of the Bukachacha coals is lower than that of the Lenin coals, but higher than that of the Jurassic coals of Kuzbass. The Bukachacha coals may therefore be assigned to hard coals, but ones comparatively weakly coalified. This has a decisive imprint on the properties and petrographic composition of the coals. Owing to the low degree of maturity of the hard coals of the Bukachacha deposit, differentiation into petrographic constituents is weaker here than in more highly coalified coals.

The few mineral formations occur in all varieties. They are represented chiefly by films of gypsum, and more rarely of calcite, situated along the cracks of parting. In addition, very thin films of white and brown clayey substance are observed. All these mineral formations occur as thin films along parting cracks. Grains of marcasite, as well as films of iron oxides, are encountered quite rarely. In dull coal one may suppose the presence of very fine clayey particles distributed within the coal mass.

B. Microscopic characterization

Microdescriptions of vitrinite and fusinite have already been given above, and assumptions regarding their genesis have also been expressed. Therefore there is no need to dwell on them here.

to dwell on it a second time. It remains for us to describe the microstructure of the remaining macropetrographic constituent parts of the Bukachacha coals.

Before describing each macroscopic constituent part separately, it should be noted that in the more dull interbeds of the Bukachacha coals the content of formed components in the attrinites increases, the role of interbeds of vitrinite, often interstratified with attrinites, decreases, and the amount of semifusinite, on the contrary, increases. In all varieties of the Bukachacha coals—lustrous striated, semilustrous, semidull, and dull—we may encounter, for example, sporinite attrinite or cuticulite attrinite, as well as sporinite-semifusinite or resinite-sporinite attrinite; but the degree of their saturation with formed components in the duller coals will be greater, while the content of structureless mass, on the contrary, will be less than in the interbeds of the more lustrous coal.

In addition, in the duller interbeds of coal the content of semifusinite and fusinite increases. Quite often an increase in the absolute dimensions of these components may be observed here. Not infrequently they attain such a size that they may be regarded as independent lenses and interbeds not included in the composition of the attrinites. In these cases semifusinite and fusinite play the same role in the composition of coal interbeds as do the attrinites.

It should be noted that the dullness of certain interbeds of the Bukachacha coals may be due to both of the indicated causes, acting either independently of one another or in combination. Let us also mention that the dullness of certain interbeds is caused by an increase in their content of mineral impurities.

a. Lustrous striated coal in the Bukachacha coals, as is evident from Table 2, possesses a more or less homogeneous texture. Lustrous coal with a homogeneous texture is composed chiefly of attrinites very weakly saturated with formed components. Here we often see resinite-sporinite and cuticulite attrinites, very weakly saturated with formed components. Cuticulite attrinite is sometimes represented by bukachachinite. Thus, the luster of this coal is due to the high content of structureless humic mass, weakly saturated with formed components.

Lustrous coal with a banded texture is characterized by the following microscopic composition and structure. Its banding is due to the alternation of broader interbeds of vitrinite with various attrinites, somewhat more strongly saturated with formed components than in the case of homogeneous lustrous coal, but still belonging to weakly saturated attrinites, in which the content of formed components is less than 50% of the total volume of the attrinite. In narrow interbeds of attrinites, interstratified with vitrinite and more rarely with semifusinite, one may observe sporinite attrinite, sporinite-semifusinite attrinite, and bukachachinite.

The samples of seam II from the northern crosscut of mine I bis, the coal interbed from 274.9 m of borehole 11, and the coal from shaft No. 2 (Zherekhova) are composed of lustrous striated coal.

b. Semilustrous coal may be distinguished in two subvarieties—semilustrous coal without ocular separateness, and semilustrous coal with well-pronounced ocular separateness. Semilustrous coal with ocular separateness is distinguished by the presence of a larger number of resin bodies or oval indeterminate formations. Probably these formed components are connected with the ocular separateness of the semilustrous coal. In addition, semilustrous coal with ocular separateness is distinguished by a greater content of semi-

fusinite. Most likely, this coal is transitional from typical semilustrous coal to semidull coal.

Semilustrous coal lacking ocular separability is characterized as follows. The varieties of this coal that have a homogeneous texture consist almost exclusively of attrinites—sporinite-cuticulitic attrinite, containing rare grains of resin, or sporinite-semifusinitic attrinite—somewhat more strongly saturated with formed bodies than the attrinites of homogeneous lustrous coal. In addition, in some attrinites here one may observe, with a decrease in the content of organic formed bodies, a certain increase in mineral impurities.

Banded semilustrous coal, lacking ocular separability, occurs in three types. The first consists of interlayers of structural vitrinite and broader interlayers of attrinites. The attrinites are represented by sporinite and sporinite-semifusinitic types. The degree of their saturation with formed bodies is greater than in the attrinites of banded lustrous coal, while the width of the vitrinite interlayers is smaller. The second is composed of alternating rather broad interlayers of vitrinite, less broad bands of semifusinite and sporinite attrinite. The third is a complex of rather broad interlayers of vitrinite, whose width is no less than the width of the interlayers of this component in banded lustrous coal, alternating with narrow interlayers and lenses of semifusinite and fusinite. Probably the presence of interlayers, lenses, and fragments of fusinite and semifusinite has a stronger influence on the increase in dullness than the other components.

Semilustrous coal lacking ocular separability comprises 3 samples from seam I, namely: from the southern drift of mine I bis, the southern drift of mine II bis, and furnace 18 of mine 2 Kapitalnaya—and one sample from seam II bis from the northern drift of mine II bis.

Semilustrous coal with ocular separability also has either a more homogeneous or a banded texture. The former consists of diverse attrinites and arborinite, as well as lenses of semifusinite. Some attrinites are more strongly saturated with formed bodies than in lustrous coals.

The more banded semilustrous coal consists of alternating bands and lenses of structural vitrinite, sporinite-resinite and sporinite-semifusinitic attrinites, bukachachinite, and semifusinite. There is less vitrinite here than of the other ingredients. In the attrinites and near lenses of semifusinite there occur oval, indistinct formations described above. Small fragments of semifusinite, sometimes observed in large quantity, locally coarsen and occupy the position of independent lenses. In the sporinite-semifusinitic attrinite there is a variable predominance now of spores, now of xylfusinite fragments. Here and there in the structureless mass of the attrinites, small areas of arborinite occur, as well as areas of structural vitrinite. The main humic mass often has a lumpy structure. It is also interesting to note that around resin bodies included in the composition of resinite attrinite or forming, together with spores and fragments of semifusinite, more complex attrinites, the structureless humic mass becomes darker. This may be explained by selective polishing: when the structureless mass next to resin bodies is less strongly ground away, its darker color is then a consequence of the greater thickness of the polished section. It is possible, however, that the change in color of the structureless mass is caused by a change in its chemical composition, depending on the co-

Morphological features of the macro-petrographic constituent parts of the Bukachacha coals.

Table 2.

resin bodies. The latter may be significant for explaining the genesis of the vitrainic separateness.

The following specimens are classified as semi-bright coal with vitrainic separateness: one specimen from seam I (from borehole 11, depth 276 m), three specimens from seam II (borehole 11, depth 254 m, and borehole 11, depth 255.7 m, as well as borehole 1, depth 276 m), and two specimens from seam II bis (borehole 38 and borehole 11, depth 221 m).

Thus, homogeneous semi-bright coal differs from bright homogeneous coal by a somewhat higher content of shaped formations in the attrinites. The type of attrinites, according to the character of the shaped formations, may be the same in both bright and semi-bright coal. However, in semi-bright coal we nevertheless more often find resinous attrinite, as well as sporinite-semifusinite attrinite, in which fragments of semifusinite predominate.

It should also be noted that the attrinites of semi-bright coal sometimes contain more finely dispersed mineral impurities. In addition, in semi-bright coal we observe rather large lenses of areas of woody semifusinite (xylinite) and indeterminate formations.

Semi-dull coal is less widespread in the examined specimens of the Bukachacha coals than semi-bright coal, but more widespread than bright and dull coal.

Semi-dull coal is characterized by an even higher content, than in semi-bright coal, of semifusinite and woody arborinite, as well as of sporinite-semifusinite attrinite. In the latter, fragments of semifusinite usually predominate over spores. All this is characteristic of semi-dull coal with a homogeneous texture, which occurs more often than the banded type.

Semi-dull banded coal consists of bands of vitrinite and of various attrinites, fairly strongly saturated with shaped formations. The vitrinite bands here are usually less wide than the attrinite bands. Among the attrinites in semi-dull banded coal the following occur: sporinite-cutinite, resinous-sporinite, and especially often sporinite-semifusinite.

Three specimens of semi-dull coal belong to seam II (the southern drift of mine II bis and the northern drift of mine II bis), one specimen to seam O (the southern drift of mine II bis), and one specimen to seam III (borehole 11, depth 187 m).

Dull coal in the examined specimens of the Bukachacha coals occurs rather rarely. This coal also has either a banded or a homogeneous texture. In the more homogeneous varieties of dull coal, sporinite-semifusinite attrinite is observed, strongly saturated with shaped formations (Figure 2), alternating with bukachachinite enriched with mineral impurities and with lenses of semifusinite.

Banded dull coal consists of broad interlayers of attrinites rich in shaped formations and narrow interlayers of vitrinite. In addition, rather broad bands of fusinite can be seen here, alternating with sporinite attrinite (Figure 5).

Thus, dull coal is characterized by a large number of shaped formations in the attrinites, a significant content of broad lenses of xylinite and fusinite, as well as an increased content of mineral impurities in the attrinites.

It should be noted that the dullness of coal may be caused not only by the combined influence of the sum of factors determining dullness, but also by each factor separately. For example, in dull coal we may encounter attrinites weakly saturated with organic form—

mineral formations, but these attrinites will instead be enriched with mineral impurities. On the other hand, low-ash matte coals are encountered that contain very many organic formed constituents. In addition, matteness may be caused by a considerable content of semifusinite and fusinite lenses and their fragments.

IV. CONCLUSION.

The Bukachacha coals are composed of vitrite, bright striated coal, semibright coal, as well as semimatte and matte coals. Most often among the samples studied one encounters semibright and semimatte coal, while vitrite, bright, and matte coal occupy a subordinate position. Thus, seam 0 is represented by semimatte coal; seam I by semibright and matte coal; seam II by the most varied varieties, beginning with vitrite and ending with matte coal, but among them semibright and semimatte coal also predominate; all samples of seam II bis are semibright coal; and those of seam III are semimatte coal.

In the microscopic composition of the Bukachacha coals, an important role is played by structureless mass, the content of which is especially abundant in bright and semibright coal, where vitrinite is also often encountered. However, portions of cellular tissue that have preserved the cellular structure or only the general structure of wood (semifusinite and arborinite) play by no means the least role in the composition of the Bukachacha coals. Of great interest is the finding in the Bukachacha coals of conifer needles, whose botanical nature it has been possible to establish with sufficient certainty. This needle material in places forms accumulations and composes partings of coal. Such portions have been called bukachachinite.

Among the formed constituents, cemented by a structureless mass and thus entering into the composition of attrinites, spores, resin bodies, cuticles, and fragments of semifusinite are often encountered.

Resin bodies sometimes very richly saturate certain coal partings and give typical liptobioliths.

Comparing the microscopic composition of bright, semibright, semimatte, and matte partings, it must be pointed out that from bright partings to matte ones the content of formed constituents in the attrinites increases; the content of semifusinite, and sometimes also of mineral impurities, likewise increases.

The material studied permits several remarks to be made on the genesis of the Bukachacha coals. Of course, to resolve certain questions of the genesis of the coals, further investigations of more extensive material are still needed, as well as observations at the site of occurrence of the seams. This is especially necessary for clarifying the conditions of accumulation of the initial material and the environment in which decomposition of the initial material took place. Therefore the considerations on the genesis of the Bukachacha coals set forth below will still be subject to correction. Nevertheless, I consider it necessary already now to present some materials on these questions, since they may facilitate further investigations.

Initial material. In the composition of the Bukachacha coals there take part: structureless humic mass, cellular tissue of wood, needles, torn cuticles, resin bodies, and spores. In the products of maceration we find tracheid tissue with bordered pits and pollen of conifers (especially abundant), cycads and horsetails?, as well as various other brevispores, whose assignment to particular plants has not yet been established. From the abundant content of conifer pollen and needles it may be accepted that a significant role in the formation of Bu-

of the Bukachacha coals belonged to conifers, whose woody tissue we often find in these coals.

However, it was not only conifers that took part in the formation of the coals. The presence of diverse spores of other plants, often still undetermined, as well as the considerable participation in the composition of the Bukachacha coals of a structureless mass which probably formed to a significant extent from the soft parts of herbaceous plants, make it quite possible to assume that the latter played a significant role in peat formation.

Conditions of accumulation. This question is difficult to elucidate correctly without field observations. However, some data from microscopic study deserve attention, and should be mentioned.

The good preservation of needles, spores, etc., and also the small content of mineral admixtures, which are either epigenetic (films of gypsum, grains of sulfides, films of iron oxides, films of calcium carbonate and films of clayey substance), or constitutional, i.e. entering into the composition of the ash of plants, or, finally, brought in by wind as atmospheric dust, make it possible to speak of the autochthonous character of the accumulation of the materials. Only some small portions in the samples studied, enriched with interlayers of clayey substance, finely interbedded with the coal and containing disorderly arranged and broken fragments of plant tissues, should be assigned to the allochthon.

Thus, during the formation of the peat bogs, prolonged periods of autochthonous accumulation were sometimes replaced by brief allochthonous ones.

The character of the peat bogs was probably similar to modern bogs of a temperate climate, for example, to our Siberian moss bogs, often overgrown with sparse pine. There is no reason to think that such bogs must occupy small areas. They may also be quite extensive; let us recall Vasyugan or the more northern parts of Siberia, where peat bogs occupy enormous areas.

Let us note that the entirely correct supposition of F. F. Otten¹) concerning the tectonic origin of depressions similar to the depression of the Bukachacha deposit should be linked with the alluvial type of productive sequence (according to V. P. Vereshchagin), when coal accumulation occurred during periods of waterlogging of the valleys of rivers that flowed through the depression.

Conditions of decomposition. The considerable content in the Bukachacha coals of structureless mass, as well as of vitrinite, argues for strong water saturation of the peat bogs, since it is known that the components mentioned are formed under anaerobic conditions²). However, these conditions were not constant and were replaced by periods of greater dryness. In such periods fusinite was formed, the content of which in the studied samples is small; but under similar conditions semifusinite also formed, to which an already very substantial role belongs in the composition of the Bukachacha coals.

Sometimes the decomposition of the organic matter proceeded very energetically, and a significant part of the readily destructible organic compounds left the peat deposit in the form of gaseous compounds, while in the peat deposit there remained chiefly compounds that stubbornly resisted biochemical and physicochemical decomposition, for example, smo-

¹) F. F. Otten. Coal-bearing basins and regions of Eastern Siberia. Collection “East Siberian Coals.” 1935, p. 82.
²) Yu. A. Zhemchuzhnikov. General Geology of Caustobioliths. 1935.

clay bodies. Thus there formed interlayers of liptobiolites rich in resin, which participate in the composition of the Bukachacha coals.

“Maturity” of the coals. Judging from the reflectivity of vitrinite, the maturity of the Bukachacha coals must be regarded as close to the maturity of the Lenin coals of the Kuznetsk Basin, associated with the Kolchugino suite of Upper Permian age. The reflectivity of vitrinite in the Lenin coals proper is closest to the reflectivity of vitrinite from the stratigraphically lower beds of the Bukachacha deposit (beds No. 0 and 1), while all the remaining beds are at a lower stage of “maturity.” This is confirmed by the features of the structureless humic mass, whose color in the lower beds of the Bukachacha deposit (reddish brown) differs from its color characteristic of the overlying beds (brown and brownish-brown). The color of the structureless humic mass of the Lenin coals is also reddish-brown.

This increase in the maturity of the Bukachacha coals deserves great attention, proceeding in accordance with Hilt’s law, since their petrographic composition, in my opinion, is considerably more favorable for coking than the petrographic composition of the Lenin coals of Kuzbass. We may venture to suggest that with a further increase in the degree of “maturity,” which should be expected in the beds lying still below bed 0, the Bukachacha coals will become good coking coals. We hope for the earliest possible verification of this supposition, since all the data on the petrographic composition definitely indicate the possibility of coking the Bukachacha coals.

DESCRIPTION OF PLATES

All watercolors were executed by the artist K. N. Osheva. The sketches were made from thin sections, the plane of which is perpendicular to the line of sight.

Fig. 1. Structural vitrinite (telinite), bounded by a spore attrinite. Seam III. Magnification 190.

Fig. 2. Sporinite attrinite, strongly saturated with shaped formations. Seam II from the southern adit of Mine II. Magnification 90.

Fig. 3. Sporinite attrinite, alternating with bands of structureless mass. Seam II from Borehole 1. Magnification 100.

Fig. 4. Resinite attrinite—liptobioite. Seam II from Borehole 3. Magnification 80.

Fig. 5. Bands and lenses of fusinite, interbedded with sporinite attrinite and a structureless mass. Seam I from Kapital’naya II Mine. Magnification 140.

Fig. 6. Bands of semifusinite, interbedded with sporinite attrinite, enclosing an indeterminate formation. Seam 0 from the southern adit of Mine II bis. Magnification 130.

Fig. 7. Bukachachinite; in the center of the drawing there is a section of a conifer needle, bounded by cuticle and containing a resin body. Seam I from Borehole 6. Magnification 90.

Fig. 8. The same, but from another part of the bukachachinite interlayer. Seam I. Magnification 90.

Fig. 9. Arborinite. Seam 0 from the southern adit of Mine II bis. Magnification 80.

Fig. 10. Bukachachinite, densely saturated with cuticle and containing a considerable quantity of mineral impurities. Seam II from the northern adit of Mine II bis. Magnification 90.

Fig. 1.

Fig. 4.

Fig. 2.

Fig. 3.

Fig. 5.

Fig. 6.

Fig. 9.

Fig. 7.

Fig. 8.

Fig. 10.

1. The term “dense” is used by us as the opposite of graininess. ↩↩↩↩↩↩

2. This term, proposed by Prof. Zhemchuzhnikov, seems to me the most successful among a whole series of other terms used in the literature to denote the same changes of the coal substance (chemical age, physico-chemical age, etc.). ↩↩↩