Viewed broadly by the physical geographer, it appears as occupying the territories to the north-west of that great plateau-belt of the old continent--the backbone of Asia--which spreads with decreasing height and width from the high table-land of Tibet and Pamir to the lower plateaus of Mongolia, and thence north-eastwards through the Vitim region to the furthest extremity of Asia. It may be said to consist of the immense plains and flat-lands which extend between the plateau-belt and the Arctic Ocean, including all the series of parallel chains and hilly spurs which skirt the plateau-belt on the north-west. It extends over the plateau itself, and crosses it beyond Lake Baikal only. A broad belt of hilly tracts--in every respect Alpine in character, and displaying the same variety of climate and organic life as Alpine tracts usually do--skirts the plateau-belt throughout its length on the north and north-west, forming an intermediate region between the plateaus and the plains. The Caucasus, the Elburz, the Kopetdagh, and Paropamisus, the intricate and imperfectly known network of mountains west of the Pamir, the Thian-Shan and Ala-tau mountain regions, and farther north-east the Altai, the still unnamed complex of Minusinsk mountains, the intricate mountain-chains of Sayan, with those of the Olekma, Vitim, and Aldan, all of which are ranged _en echelon_,--the former from north-west to south-east, and the others from south-west to north-east--all these belong to one immense Alpine belt bordering that of the plateaus. These have long been known to Russian colonists, who, seeking to escape religious persecutions and exactions by the state, early penetrated into and rapidly pushed their small settlements up the better valleys of these tracts, and continued to spread everywhere as long as they found no obstacles in the shape of a former population or in unfavourable climatic conditions. As for the flat-lands which extend from the Alpine hill-foots to the shores of the Arctic Ocean, and assume the character either of dry deserts in the Aral-Caspian depression, or of low table-lands in central Russia and eastern Siberia, of lake-regions in north-west Russia and Finland, or of marshy prairies in western Siberia, and of _tundras_ in the north,--their monotonous surfaces are diversified by only a few, and these for the most part low, hilly tracts.