Page:Popular Science Monthly Volume 52.djvu/247

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EXCURSIONS OF THE GEOLOGICAL CONGRESS.

west, 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 differ-