S. of the 50th parallel appears the loess, with all its usual characters (land fossils, want ofpstratification, &c.), showing a remarkable uniformity of composition over very large surfaces; it covers both watersheds and valleys, but chiefly the former. Such being the characters of the Quaternary deposits in Russia, the majority of Russian geologists now adopt the opinion that Russia was covered, as far as the above limits, with an immense ice-sheet which crept over central Russia and central Germany from Scandinavia and N. Russia. Another ice-covering was probably advancing at the same time from the N.E., that is, from the N. of the Urals, but the question as to the glaciation of the Urals still remains open. As to the loess, the usual view is that it was a steppe-deposit due to the drifting of fine sand and dust during a dry episode in the Pleistocene period. The deposits of the Post-Glacial period are represented through-out Russia, Poland and Finland, as also throughout Siberia and Central Asia, by very thick lacustrine deposits, which show that, after the melting of the ice-sheet, the country was covered with immense lakes, connected by broad channels (the Darden of the Swedes), which later on gave rise to the actual rivers. On the outskirts of the lacustrine region, traces of marine deposits, not higher than 200 or perhaps even 15o ft. above present sea-level, are found alike on the Arctic Sea and on the Baltic and Black Sea coasts. A deep gulf of the Arctic Sea advanced up the valley of the Dvina; and the Caspian, connected by the Manych with the Black Sea, and by the Uzboy valley with Lake Aral, penetrated N. up the Volga valley, as far as its Samara bend. Unmistakable traces show that, while during the Glacial period Russia had an arctic flora and fauna, the climate of the Lacustrine period was more genial than it is now, and a dense human population at that time peopled the shores of the numberless lakes. The Lacustrine period has not yet reached its close in Russia. Finland and the N.W. hilly plateaus are still in the same geological phase, and are dotted with numberless lakes and ponds, while the rivers continue to dig out their yet undetermined channels. But the great lakes which covered the country during the Lacustrine period have disappeared, leaving behind them immense marshes like those of the Pripet and in the N.E. The disappearance of what still remains of them is accelerated not only by the general decrease of moisture, but also perhaps by the gradual upheaval of N. Russia, which is going on from Esthonia and Finland to the Kola peninsula and Novaya Zemlya, at an average rate of about two feet per century.