Page:Popular Science Monthly Volume 52.djvu/244

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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