It may easily be supposed that the boundary-line which separates the tundri from the forest zone is both indistinct and irregular. In some parts where the cold sea-winds have a wider range, the barren grounds encroach considerably upon the limits of the forests; in others, where the configuration of the land prevents their action, the woods advance farther to the north. [Illustration: 6. COAST OF NORWAY.] Thus the barren grounds attain their most southerly limit in Labrador, where they descend to latitude 57°, and this is sufficiently explained by the position of that bleak peninsula, bounded on three sides by icy seas, and washed by cold currents from the north. On the opposite coasts of Hudson’s Bay they begin about 60°, and thence gradually rise toward the mouth of the Mackenzie, where the forests advance as high as 68°, or even still farther to the north along the low banks of that river. From the Mackenzie the barrens again descend until they reach Bering’s Sea in 65° N. On the opposite or Asiatic shore, in the land of the Tchuktchi, they begin again more to the south, in 63°, thence continually rise as far as the Lena, where Anjou found trees in 71° N., and then fall again toward the Obi, where the forests do not even reach the Arctic circle. From the Obi the tundri retreat farther and farther to the north, until finally, on the coasts of Norway, in latitude 70°, they terminate with the land itself. Hence we see that the treeless zone of Europe, Asia, and America occupies a space larger than the whole of Europe. Even the African Sahara, or the Pampas of South America, are inferior in extent to the Siberian tundri. But the possession of a few hundred square miles of fruitful territory on the south-western frontiers of his vast empire would be of greater value to the Czar than that of those boundless wastes, which are tenanted only by a few wretched pastoral tribes, or some equally wretched fishermen. [Illustration: 7. ARCTIC FOREST.] The Arctic forest-regions are of a still greater extent than the vast treeless plains which they encircle. When we consider that they form an almost continuous belt, stretching through three parts of the world, in a breadth of from 15° to 20°, even the woods of the Amazon, which cover a surface fifteen times greater than that of the United Kingdom, shrink into comparative insignificance. Unlike the tropical forests, which are characterized by an immense variety of trees, these northern woods are almost entirely composed of coniferæ, and one single kind of fir or pine often covers an immense extent of ground. The European and Asiatic species differ, however, from those which grow in America. [Illustration: 8. VERGE OF FOREST REGION.]