IRKUTSK, a government of Asiatic Russia, in East Siberia, bounded on the W. by the government of Yeniseisk, on the N. by Yakutsk, on the E. by Lake Baikal and Transbaikalia and on the S. and S.W. by Mongolia; area, 287,061 sq. m. The most populous region is a belt of plains 1200 to 2000 ft. in altitude, which stretch north-west to south-east, having the Sayan mountains on the south and the Baikal mountains on the north, and narrowing as it approaches the town of Irkutsk. The high road, now the Trans-Siberian railway, follows this belt. The south-western part of the government is occupied by mountains of the Sayan system, whose exact orography is as yet not well known. From the high plateau of Mongolia, fringed by the Sayan mountains, of which the culminating point is the snow-clad Munko-sardyk (11,150 ft.), a number of ranges, 75 00 to 8500 ft. high, strike off in a north-east direction. Going from south to north they are distinguished as the Tunka Alps, the Kitoi Alps (both snow-clad nearly all the year round), the Ida mountains and the Kuitun mountains. These are, however, by no means regular chains, but on the contrary are a complex result of upheavals which took place at different geological epochs, and of denudation on a colossal scale. A beautiful, fertile valley, drained by the river Irkut, stretches between the Tunka Alps and the Sayan, and another somewhat higher plain, but not so wide, stretches along the river Kitoi. A succession of high plains, 2000 to 2500 ft. in altitude, formed of horizontal beds of Devonian (or Upper Silurian) sandstone and limestone, extends to the north of the railway along the Angara, or Verkhnyaya (i.e. upper) Tunguzka, and the upper Lena, as far as Kirensk. The Bratskaya Steppe, west of the Angara, is a prairie peopled by Buriats. A mountain region, usually described as the Baikal range, but consisting in reality of several ranges running north-eastwards, across Lake Baikal, and scooped out to form the depression occupied by the lake, is fringed on its north-western slope by horizontal beds of sandstone and limestone. Farther north-east the space between the Lena and the Vitim is occupied by another mountain region belonging to the Olekma and Vitim system, composed of several parallel mountain chains running north-eastwards (across the lower Vitim), and auriferous in the drainage area of the Mama (N.E. of Lake Baikal). Lake Baikal separates Irkutsk from Transbaikalia. The principal rivers of the government are the Angara, which flows from this lake northwards, with numerous sharp windings, and receives from the left several large tributaries.
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as the Irkut, Kitoi, Byelaya, Oka and Iya. The Lena is the principal means of communication both with the gold-mines on its own tributary, the lower Vitim, and with the province of Yakutsk. The Nizhnyaya Tunguzka flows northwards, to join the Yenisei in the far north, and the mountain streams tributary to the Vitim drain the north-east.
The post-Tertiary formations are represented by glacial deposits in the highlands and loess on their borders. Jurassic deposits are met with in a zone running north-westwards from Lake Baikal to Nizhne-udinsk. The remainder of this region is covered by vast series of Carboniferous, Devonian and Silurian deposits - the first two but slightly disturbed over wide areas. All the highlands are built up of older, semi-crystalline Cambro-Silurian strata, which attain a thickness of 2500 ft., and of crystalline slates and limestones of the Laurentian system, with granites, syenites, diorites and diabases protruding from beneath them. Very extensive beds of basaltic lavas and other volcanic deposits are spread along the border ridge of the high plateau, about Munko-sardyk, up the Irkut, and on the upper Oka, where cones of extinct volcanoes are found (Jun-bulak). Earthquakes are frequent in the neighbourhood of Lake Baikal and the surrounding region. Gold is extracted in the Nizhne-udinsk district; graphite is found on the Botu-gol and Alibert mountains (abandoned many years since) and on the Olkhon island of Lake Baikal. Brown coal (Jurassic) is found in many places, and coal on the Oka. The salt springs of Usoliye (45 m. west of Irkutsk), as also those on the Ilim and of Ust-Kutsk (on the Lena), yield annually about 7000 tons of salt. Fireclay, grindstones, marble and mica, lapis-lazuli, granites and various semi-precious stones occur on the Sludyanka (south-west corner of the Baikal).
The climate is severe; the mean temperatures being at Irkutsk (1520 ft), for the year 31° Fahr., for January - 6°, for July 65°; at Shimki (valley of the Irkut, 2620 ft.), for the year 24°, for January - 17°, for July 63°. The average rainfall is 15 in. a year. Virgin forests cover all the highlands up to 6500 ft.
The population which was 383,578 in 1879, was 515,132 in 1897, of whom 238,997 were women and 60,396 were urban; except about 109,000 Buriats and 1700 Tunguses, they are Russians. The estimated population in 1906 was 552,700. Immigration contributes about 14,000 every year. Schools are numerous at Irkutsk, but quite insufficient in the country districts, and only 12% of the children receive education. The soil is very fertile in certain parts, but meagre elsewhere, and less than a million acres are under crops (rye, wheat, barley, oats, buckwheat, potatoes). Grain has to be imported from West Siberia and cattle from Transbaikalia. Fisheries on Lake Baikal supply every year about 2,400,000 Baikal herring (omul). Industry is only beginning to be developed (iron-works, glassand pottery-works and distilleries, and all manufactured goods are imported from Russia. The government is divided into five districts, the chief towns of which are Irkutsk (q.v.), Balagansk (pop., 1313 in 1897), Kirensk (2253), Nizhneudinsk and Verkholensk. (P. A. K.; J. T. BE.)
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