The problem of transgressive and regressive phenomena in the accumulation of sediments entered a new phase. This was due to the study of coal-bearing formations with regard to the cyclic nature of their structure. In lithologic works on the Kuznetsk, Karaganda and other basins, and especially on the Donetsk basin, the importance of sedimentary cycles consisting of regressive and transgressive parts became clear. It was further established that regression does not repeat in reverse order the rocks and facies of the transgressive part of the cycle. It is characterized by a number of facies with special features, if even they develop at the same depths and the same distances from the shore as the transgressive facies. The respective rock features also bear the features of differences that are more and more revealed.

The problem of the preconditions of coal formation needs periodic revision because of the continuous progress in the various fields of geological science and the critical testing of many of its positions on the basis of a dialectical outlook and historical comparison. Many things in coal geology that were constant and fixed in the provisions of Western European manuals and seemed immutable and that were derived from the study of Middle Carboniferous coal in practice turned out to be incomplete, one-sided and wrong in the application to coal accumulation of younger coal-bearing epochs.When considering the whole variety of coal basins of different ages, it is striking, first of all, the variability of conditions favorable to coal accumulation from period to period. The idea of some standard optimal conditions and necessary prerequisites of coal formation should be discarded and replaced by the idea of irreversible development of these prerequisites in time and space.

When drawing detailed geological maps with a hatched and, moreover, complex legend, difficulty usually arises in selecting symbols that ensure a sharp separation of individual geological horizons. Often, even in important publications, one can encounter unsuccessful so-called "blind maps". This reduces the quality of the book's design and interferes with the clear perception of the illustrations. The selection of the most successful symbols to a certain extent always remains a matter of art and experience for map compilers and draftsmen. But in this matter, knowledge of some basic, simple principles that allow one to avoid at least elementary errors when drawing maps can also help. This article outlines a number of general principles for combining symbols that should not be overlooked in the interests of the greatest clarity of maps. Hatched symbols can be arranged in a row with increasing or decreasing density of dark coloring. For this, it is advisable to use a combination of two, three or four of the above-mentioned methods of contrasting - differences in thickness, distance and direction between lines (or icons). The greatest effect is achieved by using all four differences, in particular the proximity of black and white. These differences must be combined so that each new addition to a given designation acts in one direction. The use of dotted lines and figured signs is subject to the same laws, i.e. they must also combine differences in direction, distance, and thickness or boldness of the signs.

For specialists in coal geology, foredeeps acquired special interest after the connection of these structures with coal content became indisputable. Establishing this connection was complicated by the fact that some authors classified foredeeps as platforms, others as geosynclines, and finally, others, not without some justification, classified them in a new, special (third) category, equivalent to a geosyncline and a platform, calling it a transitional region. It was necessary to clarify this complex, purely tectonic issue, which contains a number of contradictions and misunderstandings caused in part by the inaccuracy of definitions and distinctions between various concepts. This article does not pretend to introduce any new tectonic concepts or provisions. It aims to analyze existing ideas about foredeeps from historical, geological and logical positions. In an effort to understand the issue of the position and development of foredeeps, the author tries not to lose sight of the verification of abstract reasoning by connection with coal-bearing capacity and practice. The article poses a number of elementary questions to tectonists in the hope that they will express their final point of view and bring to completion those thoughts that were expressed only preliminarily.

The issues of genetic classification and typification of coal basins are of great fundamental and practical importance. The value of such a classification will depend on the significance of the principles underlying it, on its applicability in practice and on the possibility of making a more or less complete forecast based on it. Since the appearance of G. A. Ivanov's classification of coal basins, it can be considered established that the geotectonic principle is the first and most essential for genetic subdivisions into large groups. Fifteen years after the appearance of this classification, the study of geotectonic structures now allows us to make a more detailed subdivision based on the same geotectonic principle. However, this does not exclude the possibility and necessity of having other classifications of coal basins for different purposes, based on completely different criteria. For example, basins have long been divided into parallic and limnic based on the ratio of coal-bearing sediments to the proximity of the sea. This is, so to speak, a paleogeographic division. From the point of view of exploration and study, it is important to subdivide coal basins into open, semi-closed and completely closed based on the development and preservation of the rocks covering the coal-bearing strata. For the needs of geophysical work, they can be classified by the nature of tectonic forms, i.e. by the type of dislocations, as P. I. Stepanov does. Basins can be divided into brown coal and hard coal by the quality of coal, and by age into Carboniferous, Permian, Jurassic, Tertiary, etc.

In the petrographic study of coals, one has to deal with a number of concepts and terms that change their meaning over time as science develops. Therefore, at each stage of the development of coal petrography, as in any other scientific field, there is a need to revise the terminology used, clarify concepts, and establish a connection between different groups of terms. Among the current issues of coal petrography that require clarification, one of the first is the issue of macro- and microstructure and their relationship. Then comes the issue of the relationship between structure and texture, which is sometimes understood in different ways. Next comes the issue of the material composition of coals and its relationship with structure and other factors. Finally, the most difficult problem arises in linking genetic concepts with structure and texture. To do this, it is necessary to consider these issues comprehensively, in their relationship and in development, since structural differences and material changes can be considered at different stages of the development of coal matter (brown coal - anthracite).

The problem of metamorphism and transformation of coal matter is very complex. It involves questions of chemical transformation of organic matter in nature, on the surface and in the interior of the earth, questions of physical changes in coal matter under different conditions, questions of the impact of geological agents (temperature, pressure, mineralizers) and a number of others. Therefore, scientists of different specialties approach these questions somewhat differently and, based on different premises, often come to opposite conclusions. At the same time, sometimes what is only a hypothesis is presented as facts, and ignorance of factual material from a neighboring field of science sometimes leads to the denial of well‑known facts and conclusions of this science on this issue. That is why the problem of coal metamorphism still remains unsolved. All these difficulties could be overcome if a comprehensive work on this problem was set up, which would include the joint development of all controversial issues by scientists of different specialties.

At present, it can already be considered sufficiently clear that coal-bearing strata represent unique geological polyfacial formations, appearing in the history of Earth under certain conditions. By a number of characteristic features, they differ sharply from other equally typical formations, for example, flysch, molasse, salt-bearing, etc. However, the conditions of formation, as well as the very nature of coal-bearing deposits, do not remain constant for all geological periods, but, on the contrary, reveal changes and development. This development for large segments of geological history reveals its progressive nature, although it experiences periodic fluctuations and deviations, reflecting in this sense the general course of development of Earth. The present work sets as its task, by analyzing a wide range of material, to reveal the features of coal-bearing sediments, as a certain type of deposit, and to illuminate the patterns of their accumulation; and on the basis of the latter, to outline specific methods of study, arising precisely from their characteristic features, not inherent in many other complexes of deposits.

The issue of coal provinces is of great practical importance. It is closely related to forecasts in the search for new or abandoned coal deposits and the prediction of possible qualities of coal in unexplored areas. Therefore, not only coal geology is interested in establishing coal provinces, but also prospecting and exploration and the coal industry. This issue can only be correctly resolved as a result of a thorough comparative study of coal basins and the generalization of individual coal occurrences into a single whole. However, it cannot be separated from the discussion of the scope and of larger and smaller subdivisions than the province. The next and smaller subdivision unit is the coal basin. A province consists of several basins and isolated deposits. The basin itself is divided into a number of regions and deposits. The boundaries of these concepts are quite clear. The issue of larger units of the coal hierarchy is much less developed. Academician P. I. Stepanov introduced the concept of coal accumulation belts into science. By coal accumulation belt he means that "...area of the earth's surface within which, during a certain geological period, the most abundant accumulation of carbonaceous deposits and coal masses occurred."

Currently, in the Kuznetsk basin, the boundary of productive (Yerunakovskaya, Balakhonskaya) and unproductive formations and subformations is considered to be the last or first layer of working thickness (more than 0.70 m). However, recently a lot of data has accumulated that contradicts this assumption. The paleontological division will not coincide with the industrial one. A more objective criterion could be a quantitative, i.e. statistical, approach to various lithological features. Based on the idea of the cyclic structure of coal-bearing strata and knowing the differences between the typical cycles of the Ilyinskaya and Yerunakovskaya subformations, primarily in scale, we made an attempt to statistically test changes in the average and maximum thickness of cycles in a specific section. Statistical, i.e. quantitative, analysis of a number of lithological characteristics (mainly thickness) reveals the possibility of establishing a sharp and fundamental boundary corresponding to a sharp change in the average amplitude of cycles. Other features of the cycles are closely and genetically related to this change, for example, the thickness of the basal sandstones of the continental facies, the thickness of coal seams, and therefore a sharp increase in the number of working seams, i.e. purely practical consequences. This allows us to recognize that it is more rational to draw the boundary of two subformations, Ilyinskaya and Yerunakovskaya, on the basis of the cyclicity of about 41 layers, which has a number of advantages (see the article).

The geological and historical features of coal-bearing strata undoubtedly depend on the previous development of the face of the earth and on the nature of the movements at the corresponding time. In other words, they are a function of geotectonic and paleogeographic conditions. The multiple appearance of alluvial fans and proluvial, river-washed pebbles is especially characteristic only of the Lower Jurassic coal accumulation period in the USSR. The establishment of a special type of coal accumulation in the Lower Jurassic period in the Hercynian mountain country of Western Siberia, Kazakhstan and Central Asia is of great fundamental importance.

The study of schistousity of rocks of organic (more correctly — mixed) formation, such as a solid kaustobiolithes, has been shown a known community of its formation with the schistousity of a clastic rocks. This community greatly depends upon the irregularity of bearing and sedimentations of organic, as well as inorganic material, i. e., upon the difference of material composition of layers. Though, equally with this schistousity of coal, there are specific particularities attributed only to the combustible minerals. They are connected with a considerable decrease of material and volume, as well as condensation at the time of humification and carbonization, beginning from a green peat up to the antracite; corresponding cypher of this variation could be estimated as about 5-7. Horizontal deposition of a vegetable remains is partly connected with this phenomenon. The schistousity of allochthonous and autochthonous coal should be in a certain degree distinguished in the way that it is more pronounced in the first one: though this question is not yet settled. The schistousity of sapropelites has, naturally, some difference, as far as it is not connected with the conditions of deposition at the place of growth but “under place”, i. e. by means of a falling out from the suspended position according to the law of falling of small particles. As far as leptobiolites is concerned, they have a tendency to get a massive constitution. Comparing the schistousity with the other physical properties of coal, we see that it is connected with the same factors as with a nature of coal, quantity of ashes and a degree of carbonization. Schistousity, its character, formation and a degree of development are closely connected with the conditions of formation of coal itself. These factors can be used as a substantial material for the interpretation of coal.

Observations on the forms and character of cross-bedding led me to pose the question of whether they might serve as a criterion for recognizing the genesis of this stratum. The objectives of this work are: 1) to arouse interest and outline a program for detailed and thorough observations on the highly distinctive phenomena of cross-bedding; 2) to indicate an approach to their interpretation (given the current state of our knowledge); and 3) by applying these general considerations to observed specific cases, to raise the question of the possible elucidation of the genesis of the coal-bearing stratum of the Moscow Basin and of continental deposits in general, through the study of the character of stratification.