It is owing to these leading orographical features—divined by Carl Ritter, but only recently ascertained and established as fact by geographical research—that so many of the great Rivera. rivers of the old continent are comprised within the limits . of the Russian empire. Taking their rise on the plateau formation, or in its outskirts, they flow first along lofty longitudinal valleys formerly filled with great lakes, next they cleave their way through the rocky barriers, and finally they enter the lowlands, where they become navigable, and, describing wide curves to avoid here and there the minor plateaus and hilly tracts, they bring into water-communication with one another places thousands of miles apart. The double river-systems of the Volga and Kama, the Ob and Irtysh, the Angara and Yenisei, the Lena and Vitim on the Arctic slope, and the Amur and Sungari on the Pacific slope, are instances. These were the obvious channels of Russian colonization. A broad depression—the Aral-Caspian desert—has arisen where the plateau formation reaches its greatest altitude, and at the same time suddenly changes its direction from N.W. to N.E. This desert is now filled to only a small extent by the salt waters of the Caspian Aral and Balkash inland seas; but it bears unmistakable traces ott having been during Post-Pliocene times an immense inland basin. There the Volga, the Ural, the Syr-darya and the Amu-darya discharge their waters without reaching the ocean, but they bring life to the rapidly desiccating Transcaspian steppes, and link together the most remote parts of Russia. Geology.—The most striking feature in the geology of Russia is its Boundaries. remarkable freedom from disturbances, either in the form of mountain folding or of igneous intrusions. Over the greater part of the oeuonian Silurian d other Poiesoroic Rocks of the Caucasus -Cambrian MstamorphioSPlutonlo Rocks (. ~.I6 Volcanic Rocks of M. Cauca.,on region country the strata are still nearly as flat as when they were first laid down, and the deposits, even of the Cambrian period, are as soft as those of the Mesozoic and Tertiary formations in England. Only in the Urals, the Caucasus, the Timan Mountains, the region of the Donets coalfield, and the Kielce Hills is there any sign of the great folding from which nearly the whole of the rest of Europe has suffered at one time or another. In the early part of the Palaeozoic era only the gneissic region of Finland and Olonets and probably the Archean mass of S. Russia remained constantly above the sea; but there were several oscillations. Gradually, however, the sea retreated from W. Russia and in the Upper Carboniferous and Permian periods it was confined to the E. At the beginning of the Mesozoic era the whole country became land, bearing upon its surface the salt lakes in which the Trias was laid down. During the Jurassic period the sea again invaded the region, both from the N. and from the S., but still the W. of Russia rose above the waves.