Popular Science Monthly/Volume 52/December 1897/Excursions of the Recent International Geological Congress
|EXCURSIONS OF THE RECENT INTERNATIONAL GEOLOGICAL CONGRESS.|
By Prof. DANIEL S. MARTIN.
THE recent meeting of the International Congress of Geologists at St. Petersburg has led incidentally to an important series of publications regarding the geological features of a large portion of European Russia, the Urals, and the Caucasus. Everything connected with the meeting was arranged upon a most extensive and liberal scale, and especially the great series of excursions before and after the congress. For these there was prepared a set of handbooks, describing the leading points of geological structure and economic importance, and bringing together a great body of results of recent study, either unpublished before or scattered through various Russian and German periodicals and transactions, and practically inaccessible to the ordinary student. These handbooks or "guides" were prepared with great care by a number of prominent Russian geologists, who divided the routes of the excursions into sections, and went over them in detail during the previous year. When completed the reports were translated into French (a few into German) and beautifully printed as octavo pamphlets. These, to the number of thirty-four, were bound together in a volume of six hundred and forty-eight pages, with a spring cover, such that each paper could be taken out and used separately during that part of the journey which it described.
The general editor, Prof. Th. Tschernytschew, observes, in his very modest introduction, that this is the first publication of the kind that has been issued in Russia; and while it can not be placed in comparison with such great general works as have appeared in other lands, like Oldham's Geology of India, Woodward's Geology of England and Wales, or Lepsius's Geologie von Deutschland, he hopes that it may yet present to students a more complete and " up-to-date" outline of the geological features of Russia than has before been attainable.
The volume was prepared for members attending the congress and presented to them. The very few copies that have reached this country have been brought by American delegates who have lately returned. Whether, or how far, the work will be procurable hereafter through any ordinary channels does not yet appear. It is to be hoped, however, that at least our scientific institutions and libraries may be able to secure copies of so valuable a treatise.
The general outline of the excursions was as follows: During the month prior to the meeting, a journey to the celebrated mining and mineral regions of the eastern Urals, the route being from Moscow by rail south and east, by Penza to Oufa, passing through the Urals to Zlatoust; then by the Ural Railway, which runs parallel to the mountains on the Asiatic side, north to Ekaterinbourg and the mining district of Tagilsk; thence recrossing the Urals to Perm, and from there by steamer down the Kama and up the Volga to Nijni Novgorod and back to Moscow by rail.
After the congress another great trip was arranged for—to southern Russia, the Caspian, the Caucasus, and the Crimea; this comprised several selections or "variants." The main route was from Moscow to Vladikavkaz in the Caucasus, one section going by rail through the valley of the Don; another proceeding by Kiev and taking the Dnieper valley; and a third going to Nijni Novgorod, and by steamer down the Volga to Astrakhan and on the Caspian Sea to Petrovsk; and all meeting at Vladikavkaz. From this point the route led by the great military road of Georgia, south to Tiflis, and thence to visit the oil deposits at Baku on the Caspian, returning by Tiflis to Batoum on the Black Sea, and by steamer to the Crimea, the excursion breaking up at Sebastopol.
A number of side trips to points of special interest were further associated with these excursions, and there were also two shorter excursions—one to Esthonia and one to Finland—for the study of early Palæozoic and Archæan rocks and glacial deposits.
These outlines are necessary in order to give an idea of the extent of country covered by the series of guidebooks that compose this notable volume. The first monograph is a description of the geology of Moscow and its environs, by Professor Nikitin; the last, by Prof. F. Schmidt, deals similarly with the vicinity of St. Petersburg. The remaining thirty-two take up seriatim the districts traversed by the several excursions and "variants." Nearly all of them are freely illustrated with sections, maps, diagrams, etc.; some have interesting views and photographs, and the more important have complete references or bibliographies of the previous work done in the regions described.
All that can be attempted in a brief outline like the present is to indicate the general scope of the principal papers, and to refer to certain points presenting special interest.
Following the general course of the first excursion, which is all that can be done in the present article, we have three papers on the geology of the route through central and eastern Russia to the Ural Mountains. Much of this great region has been little studied since the classic researches of Murchison, save that in recent years several Russian geologists have been engaged upon it at various points; but their work is largely inaccessible, and much of it is not yet published. Article No. 1, on the environs of Moscow, and No. 2, from Moscow to the city of Oufa, are by Prof. S. Nkitin; No. 3, by Professor Tschernitschew, covers the route from Oufa to the eastern slope of the Urals.
In the whole vicinity of Moscow the general section gives, beneath the modern surface deposits, two well-marked Quaternary divisions, resting upon Cretaceous beds (Neocomian and Aptian), and these upon an important body of what Nikitin has termed Volgian deposits, upper and lower. Beneath these are Jurassic beds (Kimmeridgian to Callovian inclusive), underlaid by Carboniferous strata of the stage called here Moscovian. The Quaternary deposits consist of a widespread morainic bowlder clay, unstratified, and filled with transported stones from Finland and northern Russia; westward this passes directly into the lower "Geschiebelehm," or Saxonian bowlder clay, of the Germans, and is the product of the great Russo-Scandinavian ice sheet. Above this is an unstratified bowlder sand, and below it lies a stratified bowlder sand, the latter containing a larger proportion of material from the rocks of the vicinity. Professor Nikitin holds strongly that here, and through the whole of central Russia, there was but one period of ice-covering and moraine deposit, with no indications of repeated advances or of interglacial beds. The upper bowlder sands he refers to the period of retreat of the great Russo-Scandinavian glacier, and attributes them to the action of streams and melting ice.
The chief point of novelty and interest, however, in this Moscow section is the relation of the upper and lower Volgian beds, which are important formations over a very large area. They have been variously considered by different explorers of late, some regarding them as lower Cretaceous, and others as upper Jurassic. Their stratigraphic position is clear; their fauna shows marked Jurassic relations at the base and Neocomian relations in the upper portions. Professor Nikitin regards them as a distinct series, lying between the upper Jurassic and the Cretaceous and connecting the two; so that there is not in Russia any such gap between these systems, in his view, as is recognized in western Europe. The fauna, however, requires more detailed study before positive results can be assured. He gives much space to this discussion, in which we can not follow him here.
The Jurassic beds below present a close correspondence throughout the whole of central Russia to those of the north and west of France, and no marked differences can be observed.
The Trias and the Permian are here wanting, and the Mesozoic rocks lie directly on the limestones of the "Etage Moscovien" of the middle Carboniferous. Both are fairly rich in fossils, and at the base of the Callovian is a conglomerate in which characteristic Callovian fossils are intermingled with rolled fossils of the underlying Muscovian.
In the journey southward and eastward, from Moscow to Riazan, Penza, Samara, and Oufa, these same rocks occupy the greater part of the way, with much of interesting discussion, until some other features begin to appear as the route approaches the Volga, which it follows from Syzran to Samara. The lower Quaternary bowlder clay begins to disappear and gives place gradually to an upper series of deposits of mingled fluvial and æolian character, the most marked of which are the "loess" and a heavy "terrace clay" of the valleys, with a variety of intermediate types.
At Syzran the general uniformity of the structure is broken by an anticlinal elevation, in a north-to-south course, crossed by an important line of fault, west-northwest and east-southeast. These movements have produced a line of hills, which have deflected the course of the Volga, and are the only examples of the kind in this extensive region. Professor Nikitin places the period of their elevation in the early Tertiary.
At this point a very interesting feature first appears—the occurrence of deposits laid down by the former extension of the Caspian Sea. They are first seen near Syzran, in a baylike portion of the valley of the Syzran River, and thence become more marked in traveling eastward. They are chiefly clayey sands and conglomerates, with rolled pebbles of the underlying Cretaceous rocks. They appear on the divides and higher portions of the banks of the Volga and its affluents, and are evidently older than the "terrace clays" of the upper Quaternary. At many points they contain brackish water shells of late Caspian type. We have here the evidence of the Pleistocene extension of the Caspian waters over the great valley of the Volga as far north as latitude 53°, and even farther.
Crossing the Volga near Samara, the route enters upon a wide valley which passes gradually into the great trans-Volgian steppes. Much interesting discussion as to the peculiar soils of the steppes and their relations to geology and to tree-growth can only be alluded to. In proceeding eastward the great Permian formation, so named by Murchison, begins to appear, forming a broad band or zone stretching along the western base of the Urals. The "tchernozem" or surface soil of the steppes rests upon successively older rocks as the route passes northeastward from the Volga toward the mountains. Beneath it appear more or less of the Caspian deposits, partly overlaid and partly connected with the "terrace clay" of the Quaternary. The underlying rocks are in succession Cretaceous, Volgian, Jurassic, and Permian, as this wide area is traversed. Permo-carboniferous and Carboniferous rocks are met on entering the Urals, the lower members of each appearing successively, and, when the folds of the mountains are fully reached, a great body of Devonian.
Between Samara and Oufa, as the steppes rise, the country presents an aspect which Professor Nikitin observes as strikingly like the eroded plateau regions of the western United States. This is particularly well marked in the valley of the Dioma River, where high level regions of nearly horizontal stratified sediments have been worn down along all the drainage lines into scarped and picturesque heights, with broad, flat areas of intervening watershed—as we should call it, a country of cañons, mesas, and "mauvaises terres."
The rocks of this region are principally Permian, but the Russian geologists are not fully agreed as to the details. A great body of limestones, marls, and sandstones, definitely of upper Permian age ("Zechstein"), lies between two distinct series of "marnes irisées—red and variegated marls. The lower of these is undisputed (the "Rothliegender"), but the upper is regarded by some as also true Permian, and by others as transitional to the Triassic. For this upper series the name "Etage Tartarien" is employed.
It is interesting to note how much more continuous the geological succession appears to be here than in the west of Europe. The recognition of the Permian itself, as a whole, was an immense advance in this direction; and now we can almost trace it downward through the Permo-carboniferous and upward through the Tartarian, connecting the Palæozoic and the Mesozoic continuously. In the same way, and in almost the same region, the Volgian series appears to unite the Jurassic with the Cretaceous.
From Oufa to and through the southern Urals the description is taken up by Professor Tschernitschew. The structure of the Urals bears some marked resemblances to that of our Appalachians; the general course is much the same, north-northeast to south-southwest, and the principal character is that of a series of parallel folds, with the anticlinal crests eroded into longitudinal valleys, so that each axis of elevation produces two parallel lines of heights. Similarly, too, the disturbance increases from the west eastward, and metamorphic and intrusive rocks appear and attain a great development toward the Asiatic side. Beyond, moreover, forming a separated though intimately connected portion of the system, are the Ilmen Mountains and others that align with them, highly metamorphic, much intruded, and exceedingly rich in mineral treasures. These recall our Blue Ridge range in its geographical relation to the Alleghanies, though their connection with the Urals is much closer geologically. Finally, the Ural range, like our true Appalachians, is monogenetic—i. e., the product of a single period of elevation.
The body of the southern Urals consists of Devonian and Carboniferous beds, much inclined. The latter are principally limestones, while the former, largely also calcareous above, become more fragmental lower down. The succession of stages is very regular in each, and is discussed at length. In the lower Devonian (Hercynian) occurs a hard and heavy sandstone, which by its resistance to erosion forms generally the crests of the parallel ridges. This sandstone not only passes into quartzite, but becomes at times micaceous and takes on a distinctly metamorphic habit. Professor Tschernitschew gives a clear and detailed account of the gradual passage of this sandstone into various kinds of micaceous, talcose, and chloritic schists. In the eastern Urals intrusive rocks appear more and more, mainly granites and diabases. Of these there are again many particulars given, and especially interesting accounts of the contact phenomena, where these dikes and veins have traversed the sedimentary rocks and produced local alteration.
In regard to Quaternary deposits the remarkable fact is brought out that there are no definite traces of glaciation in the Ural Mountains south of latitude 61°. All the surface deposits are local, either the work of streams or from the decomposition of rocks in place, after the manner of our "southern drift." For this latter process and its results the words "éluvion" and "dépôts éluviales" are used in these treatises in distinction from material removed and redistributed by flowing water—a convenient and desirable term. Most of the gold placers of the Urals are of these kinds—alluvial in some places and eluvial in others, but not glacial. In some cases the auriferous gravel and sand can be traced downward almost directly into the disintegrating quartz of an outcropping vein.
The main Urals are rich in iron ores, chiefly hematite and spathic iron; in the Ilmen range the ore is magnetite and occurs in a different geological relation. The oxide and carbonate are associated with dolomitic limestones of the lower Devonian, and may be traced into them by a gradual transition, as at the mines of Bakal, where the ore is hematite for some distance below the surface, then passes to spathic iron, and this into dolomitic limestone at a considerable depth.
After traversing the Urals to Zlatoust, where are the great iron and steel works that produce some of the finest weapons used in the Russian army, and that sent an elegant exhibit to the Chicago World's Fair, the excursion traversed the famous mining and mineral region of the Ilmen Mountains northward to Tagilsk and Ekaterinbourg. This portion of the route is treated of in several papers as follows: The Eastern Slope of the Urals (No. 5), by Prof. A. Karpinsky; The Minerals of Kussa and Miass (No. 4), by A. Arzruni; The Gold Deposits of the Southern Urals (No. 6), by N. Wyssotsky; The City of Ekaterinbourg and its Environs, especially in Reference to Prehistoric Archæology (No. 7), by Dr. O. Clerc; The Mining Districts of Tagil and Gora-Blagodat (No. 9), by Professor Tschernitschew; and one or two minor articles.
Professor Karpinsky gives an admirable account of the region of the eastern Urals and beyond, emphasizing the contrast between the two sides of the system. While the western slope passes by gradual and gentle undulations into the plains and steppes of European Russia, the Asiatic side has been enormously eroded away. A wide belt of country along the eastern base of the Urals, consisting of upturned and folded rocks identical with those of the mountains, has been leveled down to an absolute plain. Over this are spread the deposits of the Tertiary sea that reached in Pliocene time nearly to the central ranges of the Urals, and that has largely obliterated their eastern portion. These deposits stretch far away into the great Siberian plain. Along their western edge, and for some distance eastward, they are strewn with lakes—some fresh and some salt; some deep and narrow among the folds of the edge of the mountain region; others broad, shallow, and with flats and benches of gradual contraction in the level country to the east. Two striking views of this lake-bestrewn plain from the top of some of the Ilmen peaks are given in the monograph.
The gold of the Urals, of course, receives much attention in these papers; the placers are carefully described, and the quartz mining also, which in some districts is overtaking and surpassing the placers in output. Closely connected with these are the platinum workings, thus far wholly surface deposits. But it is of great scientific interest to note the definite tracing of this metal to its original rock source, associated with chromic iron in serpentines, which themselves are altered peridotites. These facts are not actually new, but they are recent and little known.
Especial interest gathers around two great mineral and mining centers—Miask, at the southern base of the Ilmen Mountains, and Tagilsk, toward the northern part of the route, near Ekaterinbourg. The rocks of all this region are metamorphic and intrusive, of great variety, and are described in some detail. At times the limestones are not so changed but that they retain determinable fossils (Devonian). The Miask region is remarkable for the varied and in some cases peculiar character of its rocks and the great number of minerals contained in them; the locality is celebrated in this respect, but can not be dwelt upon here. The Tagilsk region is notable for its great iron and copper mines; the former are magnetite masses so intimately associated with porphyry that Professor Karpinsky can only regard them as of similar and contemporaneous origin. There are several great mines in and around the rather isolated porphyry hill, Mount Wyssokaia; of these the oldest is that of Nijni Tagilsk. Adjacent to it, below the hill, is the copper mine of Mednoroudiansk, which has furnished all the beautiful Siberian malachite so familiar in collections and in Russian works of art. Unfortunately, the name of the iron mine, Nijni Tagilsk, has so long been connected with the malachite that the error can scarcely now be corrected. This name, however, is that of the district as well, and so may be used for the copper locality in a general sense.
The copper ores are a later deposit, amid tufas connected with the porphyry of the hill.
From these points the railroad turns westward, crosses the main Urals, here not very elevated, and gradually descends to the city of Perm. The route traverses much the same succession of rocks, in reverse order, as was described in approaching the mountains from the east. This portion is treated of by Professor Krasnopolsky, and the steamer route on the Kama and Volga to Nijni Novgorod by MM. Stuckenberg, Nikitin, and Amalitzky. All these contain much of geological and geographical interest, but there is not space to go into further particulars.
From Nijni Novgorod, the city of the great annual fair, where fine sections of the several horizons of the Permian are directly covered by Quaternary loess-like clays, the party returned to Moscow. Here we must close this very hasty sketch, which can only give the faintest idea of the extent and interest of the tour through regions so little known and so little accessible to the majority of geological students.
- Guide des Excursions du VII. Congrès Geologique International; avec 39 planches, nombreuses figures, cartes locales et une carte géologique de la Russie d'Europe à l'échelle de 6300000 St. Pétersbourg: Imprimerie de M. Stassuléwitsch, Wassili Ostrov, 5 ligne, 28, 1897.