Siberia (5,000), a vast Russian territory in North Asia (one and a third times the size of Europe), stretching from the Ural Mountains (W.) to the seas of Behring, Okhotsk, and Japan (E.), bounded on the N. by the Arctic Ocean and on the S. by China and the Central Asiatic provinces of Russia; forms in the main an immense plain, sloping from the Altai and other mountain ranges on the S. to the dreary, ice-bound littoral on the N., drained by the northward-flowing Obi, Irtish, Yenesei, Lena, &c., embracing every kind of soil, from the fertile grain-growing plains of the S. and rich grazing steppe-land of the W. to the forest tracts and bogland of the N. and experiencing a variety of climates, but for the most part severely cold; hunting, fishing, and mining are the chief industries, with agriculture and stock-raising in the S. and W. The great Trans-Siberian Railway, in construction since 1891, is opening up the country, which is divided into eight "governments," the chief towns being Tomsk, Irkutsk, Omsk, and Tobolsk; three-fifths of the population are Russians, chiefly exiles and descendants of exiles. Russian advance in Asia against the Tartars was begun in 1850, and was carried on by warlike Cossack marauders, followed by hunters, droves of escaping serfs, and persecuted religious sects.