2. The Rocky Mountain forest, whose characteristic species are the western yellow pine (_Pinus ponderosa_), Engelmann spruce (_Picea engelmanni_) and lodgepole pine (_Pinus murrayana_). This forest is frequently broken by treeless areas of greater or less extent, especially towards the south, and it suffers greatly from fire. Subarid in character, except to the north and at high elevations, the vast mining interests of the region and its treeless surroundings give this forest an economic value out of proportion to the quantities of timber it contains. This distribution of the various forests is indicated on the first of the two accompanying maps. The second map shows the situation of the national forests hereafter mentioned. The forests of Alaska fall into two main divisions: the commercial though undeveloped forests of the south-east coast, which occur along the streams and on the lower slopes of the mountains and consist chiefly of western hemlock (_Tsuga heterophylla_), Sitka spruce (_Picea sitchensis_), yellow cedar (_Chamaecyparis nootkatensis_) and giant arborvitae (_Thuja plicata_), usually of large size and uninjured by fire; and the vast interior forests, swept by severe fires, and consisting chiefly of white and black spruces (_Picea canadensis_ and _nigra_), paper birch (_Betula papyrifera_) and aspen (_Populus tremuloides_), all of small size but of great importance in connexion with mining. Northern Alaska and the extreme western coast regions are entirely barren. [Illustration: Forest Regions of the United States _The unshaded areas are treeless, except along the Streams_]