The boreal forest presents a striking contrast to the forests of the torrid zone and to the greater portion of the forests of temperate regions in the fact that it is composed of but a few species of trees. Monotony which becomes oppressive to one who lingers long in its sombre shade is its most conspicuous characteristic. In the main it is composed of but eight species of trees, namely, white and black spruce, larch or tamarack, canoe-birch, balsam-poplar, aspen, balsam-fir, and the gray pine. Of these the spruces are the most abundant and most characteristic as well as the most northern trees of the continent. They frequently reach sufficient size to make them available for building log houses and for lumber. Four of the species mentioned above, namely, the white spruce, canoe-birch, balsam-poplar, and aspen, cross the entire breadth of the continent from Labrador to Alaska, but the pines and firs in the east and the west are of different species. The larch or tamarack, which forms such an important feature of the forest in eastern Canada and about the Laurentian lakes, extends westward to beyond Hudson Bay, but is represented by other species in the Mackenzie and Yukon basins, and in the northern portion of the Pacific mountains. The region occupied by the great northern forest is interspersed with lakes, some of them of large size, and by innumerable swamps. The spruces and the gray pine grow on the uplands between the lakes and swamps, while the cold, wet bottom-lands are occupied by poplars, dwarf birches, willows, and alders. In the north, near where the forest breaks into outstanding groves and finally gives place to grassy hills, as along the Porcupine River in Alaska, the foliage in the lowlands becomes golden in autumn and forms irregular, far-reaching avenues of brilliant colour separating the hills, which are black with spruce-trees or shimmer with the soft gray tints of ripened grasses. There is much that is beautiful and even lovely along the poleward border of the great forest, but within its deeper recesses the ground is covered with mosses and lichens, and the stiff, sombre trees have a monotonous similarity and unbending rigidity. In spite of the great area covered by the boreal forest, it being one of the greatest, if not the most widely extended continuous growth of arboreal vegetation in the world, it is of comparatively small economic importance. Even if the trees were within the reach of a market, their wood is of inferior quality and not generally suitable for lumber. A modern industry has been developed, however, which may bring it into demand, namely, the manufacture of wood-pulp, so largely employed in the making of paper and for other purposes.