The arctic lands of Eurasia and North America show two well-marked zones—a zone of treeless wastes bordering the Polar Sea, and a coniferous forest zone lying immediately to the south. The treeless wastes are known as tundras in Europe and Asia, and as barren grounds in North America. These form plains of immense extent, but of very unequal width from north to south. In Eurasia they lie for the most part north of the Arctic Circle, while in North America they range upon the whole considerably farther south, reaching the sixtieth parallel on the western shores of Hudson Bay. Their southern boundary, however, is in both Old and New Worlds exceedingly irregular. Where the flat lands are exposed to the full sweep of the northern blasts, tundra conditions advance far to the south, invading the forest zone in narrower or broader stretches. Indeed, even within the region of arctic forests isolated patches and wider areas of tundra are encountered. In other places more sheltered from the fierce winds coming from the polar seas, the arctic forests in their turn encroach upon the tundras, so as nearly to reach the shores of the frozen ocean. Such is the case in the valleys of the Yenesei, the Khatanga, the Olenek, the Lena, and other North Siberian rivers. Similarly in North America the arctic forests straggle down the valleys of the Mackenzie and other rivers to beyond the Arctic Circle.
Mosses and lichens form the prevailing vegetation of the tundras— marshes and bogs extending over vast areas in spring and summer, while the less marshy tracts are carpeted with gray lichens. Here and there, too, in sheltered spots, dwarf birch and willow scrub sprinkle the surface or flourish in denser masses, and ever and anon more or less wide stretches of meadow put in an appearance. Now and again the interminable plains give place to rolling ground, the low hills and knolls being not infrequently clothed with dwarf trees. No hard and fast line, indeed, can be drawn between the tundras and the arctic forests. The two regions not only interosculate, but numerous oases of trees are encountered in the tundras along their southern margin, while equally numerous patches of tundra, as already mentioned, are met with farther south within the arctic zone. It may be added that in northern Siberia bare rocky hills and mountains—highly fissured, and showing many gullies, ravines, and debris-strewn valleys—now and again break the uniformity of a tundra landscape.
A word or two now as to the characteristic animals of the tundras and barren grounds. First among these come the arctic lemmings. They feed on grass roots and stalks, mosses, reindeer linchens, and the shoots of the dwarf birch, for which in winter they tunnel through the turf or under the snow. The banded lemming is an especially characteristic form, since it is confined to the maritime tracts of Eurasia and the adjacent islands, and the corresponding areas of North America, and is never met with in the forest zone. The Obi lemming has a similar distribution, but ranges somewhat farther south, and not quite
