Naturally, not the whole of the vast area just discussed could be brought under cultivation, even under the most favorable conditions of rainfall. A very large portion of the territory in question is mountainous and often of so rugged a nature that to farm it would be an impossibility. It must not be forgotten, however, that some of the best dry-farm lands of the West are found in the small mountain valleys, which usually are pockets of most fertile soil, under a good supply of rainfall. The foothills of the mountains are almost invariably excellent dry-farm lands. Newell estimates that 195,000,000 acres of land in the arid to sub-humid sections are covered with a more or less dense growth of timber. This timbered area roughly represents the mountainous and therefore the nonarable portions of land. The same authority estimates that the desert-like lands cover an area of 70,000,000 acres. Making the most liberal estimates for mountainous and desert-like lands, at least one half of the whole area, or about 600,000,000 acres, is arable land which by proper methods may be reclaimed for agricultural purposes. Irrigation when fully developed may reclaim not to exceed 5 per cent of this area. From any point of view, therefore, the possibilities involved in dry-farming in the United States are immense. Dry-farm area of the world Dry-farming is a world problem. Aridity is a condition met and to be overcome upon every continent. McColl estimates that in Australia, which is somewhat larger than the continental United States of America, only one third of the whole surface receives above 20 inches of rainfall annually; one third receives from 10 to 20 inches, and one third receives less than lO inches. That is, about 1,267,000,000 acres in Australia are subject to reclamation by dry-farming methods. This condition is not far from that which prevails in the United States, and is representative of every continent of the world. The following table gives the proportions of the earth's land surface under various degrees of annual precipitations:-- Annual Precipitation Proportion of Earth's Land Surface Under 10 inches 25.0 per cent From 10 to 20 inches 30.0 per cent From 20 to 40 inches 20.0 per cent From 40 to 60 inches 11.0 per cent From 60 to 80 inches 9.0 per cent From 100 to 120 inches 4.0 per cent From 120 to 160 inches 0.5 per cent Above 160 inches 0.5 per cent Total 100 per cent