of coal, oil, natural gas (Ishimbay and Krasnokamsk areas) and potassium salts. Both slopes are rich in bituminous coal and lignite, and the largest deposit of bituminous coal is in the north (Pechora field). The specialty of the Urals is precious and semi-precious stones, such as emerald, amethyst, aquamarine, jasper, rhodonite, malachite and diamond. Some of the deposits, such as the magnetite ores at Magnitogorsk, are already nearly depleted. Rivers and lakes Many rivers originate in the Ural Mountains. The western slopes south of the border between the Komi Republic and Perm Krai and the eastern slopes south of approximately 54°30'N drain into the Caspian Sea via the Kama and Ural basins. The tributaries of the Kama include the Vishera, Chusovaya, and Belaya and originate on both the eastern and western slopes. The rest of the Urals drain into the Arctic Ocean, mainly via the Pechora basin in the west, which includes the Ilych, Shchugor, and the Usa, and via the Ob basin in the east, which includes the Tobol, Tavda, Iset, Tura and Severnaya Sosva. The rivers are frozen for more than half the year. Generally, the western rivers have higher flow volume than the eastern ones, especially in the Northern and Nether-Polar regions. Rivers are slower in the Southern Urals. This is because of low precipitation and the relatively warm climate resulting in less snow and more evaporation. The mountains contain a number of deep lakes. The eastern slopes of the Southern and Central Urals have most of these, among the largest of which are the Uvildy, Itkul, Turgoyak, and Tavatuy lakes. The lakes found on the western slopes are less numerous and also smaller. Lake Bolshoye Shchuchye, the deepest lake in the Polar Urals, is deep. Other lakes, too, are found in the glacial valleys of this region. Spas and sanatoriums have been built to take advantage of the medicinal muds found in some of the mountain lakes. Climate The climate of the Urals is continental. The mountain ridges, elongated from north to south, effectively absorb sunlight thereby increasing the temperature. The areas west of the Ural Mountains are warmer in winter than the eastern regions because the former are warmed by Atlantic winds whereas the eastern slopes are chilled by Siberian air masses. The average January temperatures increase in the western areas from in the Polar to in the Southern Urals and the corresponding temperatures in