The _tundra_ itself is in summer completely free of snow, but at a limited depth from the surface the ground is continually frozen. At some places the earthy strata alternate with strata of pure, clear ice. It is in these frozen strata that complete carcases of elephants and rhinoceroses have been found, which have been protected from putrefaction for hundreds of thousands of years. Such _finds_, however, are uncommon, but on the other hand single bones from this primeval animal world occur in rich, abundance, and along with them masses of old driftwood, originating from the Mammoth period, known by the Russian natives of Siberia under the distinctive name of "Noah's wood." Besides there are to be seen in the most recent layer of the Yenesej _tundra_, considerably north of the present limit of actual trees, large tree-stems with their roots fast in the soil, which show that the limit of trees in the Yenesej region, even during our geological period, went further north than now, perhaps as far as, in consequence of favourable local circumstances, it now goes on the Lena. [Illustration: SUB-FOSSIL MARINE CRUSTACEA FROM THE TUNDRA. ] On the slopes of the steep _tundra_ bank and in several of the _tundra_ valleys there is an exceedingly rich vegetation, which already, only 100 kilometres south of Yefremov Kamen, forms actual thickets of flowering plants, while the _tundra_ itself is overgrown with an exceedingly scanty carpet, consisting more of mosses than of grasses. Salices of little height go as far north as Port Dickson (73 deg. 30' N.L.), the dwarf birch (_Betula nana_, L.) is met with, though only as a bush creeping along the ground, at Cape Schaitanskoj (72 deg. 8' N.L.); and here in 1875, on the ice-mixed soil of the _tundra_, we gathered ripe cloudberries. Very luxuriant alders (_Alnaster fruticosus_, LEDEB.) occur already at Mesenkin (71 deg. 28' N.L.), and the Briochov Islands (70 deg. to 71 deg. N.L.), are in several places covered with rich and luxuriant thickets of bushes. But the limit of trees proper is considered to begin first at the great bend which the river makes in 69 deg. 40' N.L., a little north of Dudino. Here the hills are covered with a sort of wood consisting of half-withered, grey, moss-grown larches (_Larix sibirica_), which seldom reach a height of more than seven to ten metres, and which much less deserve the name of trees than the luxuriant alder bushes which grow nearly 2 deg. farther north. But some few miles south of this place, and still far north of the Arctic Circle, the pine forest becomes tall. Here begins a veritable forest, the greatest the earth has to show, extending with little interruption from the Ural to the neighbourhood of the Sea of Ochotsk, and from the fifty-eighth or fifty-ninth degree of latitude to far north of the Arctic Circle, that is to say, about one thousand kilometres from north to south, and perhaps four times as much from east to west.