Page:Popular Science Monthly Volume 52.djvu/246

232 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