Toward the south, the Cis-Ural, European side of the Ponto-Caspian lowland, is separated from the Black Sea by a ridge of granite knolls, which passes from Volhynia and Podolia eastward as far as the cataracts of the Dnieper, and thence southeast, with diminished breadth, reaching its limit at Taganrog, on the lower Don, and the Sea of Azof. This ridge separates the narrow steppes of the northern shore of the Black Sea from the lowland of South Russia, the fruitful district of Ukraine. The height of these hills in the west, where they appear to have the greatest elevation, has been estimated to be about 1000 feet above the sea. Toward the Dnieper they have not yet been carefully measured; but probably there they do not rise above 700 feet. The small sand steppe south of these granite hills runs from the Crimea eastward as far as the North Caucasian steppe, between the Don, Volga, and the Caspian, and indeed may be traced to the northeast as far as the Bashkiric-Ural chain. Lakes of marked saltness are found there: Elton, for instance, which lies 24 feet above the sea; while farther eastward they are found, as for example on the Kamysh and at Samara at a depression of—138 feet, 60 feet below the level of the Caspian Sea. Yet this lacks confirmation. From this lowland, only a few elevations arise, and these of insignificant absolute height; yet, on account of the extreme uniformity of the whole country, they are objects of amazement to the whole steppe world. The Little Bogdo, south of Lake Elton, and yet farther south, Great Bogdo, 504 feet above the sea, according to Humboldt, and Mount Arsargar, 331 feet in absolute height, according to Murchison, are the only important hills. The Great Bogdo is composed of calcareous limestone and of sandstone, with rich deposits of salt. The Kirgheez steppe separates, by a plain of very moderate elevation, the north Siberian lowland from the Caspian-Ural depression. It was formerly supposed, and indeed represented on the map, that a mountain range passes through this district from the Ural chain to the Altai. The Kirgheez steppe appears to range from 780 to 960 feet in elevation; while the Siberian plain is but 280 feet above the sea at Omsk, 192 feet at Tora, and 108 feet at Tobolsk. It has been considered by some that the Kirgheez steppe, as well as the granite hills of southern Russia, belong to an undeveloped system of mountains, an early cooling having solidified them before reaching the elevation which they would have attained; and that they partake of the direction which analogy would teach us such a chain would have, from northeast to southwest, parallel with the Carpathian and the Caucasus ranges.