I have already set forth my belief that Irrigation is everywhere practicable, is destined to be generally adopted, and to prove signally beneficent. I do not mean that every acre of the States this side of the Missouri will ever be thus supplied with water, but that _some_ acres of every township, and of nearly every farm, should and will be. I propose herein to speak with direct reference to that large portion of our country which cannot be cultivated to any purpose without Irrigation. This region, which is practically rainless in Summer, may be roughly indicated as extending from the forks of the Platte westward, and as including all our present Territories, a portion of Western Texas, the entire State of Nevada, and at least nine-tenths of California. On this vast area, no rain of consequence falls between April and November, while its soil, parched by fervid, cloudless suns, and swept by intensely dry winds, is utterly divested of moisture to a depth of three or four feet; and I have seen the tree known as Buckeye growing in it, at least six inches in diameter, whereon every leaf was withered and utterly dead before the end of August, though the tree still lived, and would renew its foliage next Spring. Most of this broad area is usually spoken of as desert, because treeless, except on the slopes of its mountains, where certain evergreens would seem to dispense with moisture, and on the brink of infrequent and scanty streams, where the all but worthless Cotton-wood is often found growing luxuriantly. A very little low Gamma Grass on the Plains, some straggling Bunch-grass on the mountains, with an endless profusion of two poor shrubs, popularly known as Sage-brush and Grease-wood, compose the vegetation of nearly or quite a million square miles. I will confine myself in this essay to the readiest means of irrigating the Plains, by which I mean the all but treeless plateau that stretches from the base of the Rocky Mountains, 300 to 400 miles eastward, sloping imperceptibly toward the Missouri, and drained by the affluents of the Platte, the Kansas, and the Arkansas rivers. The North Platte has its sources in the western, as the South Platte has in the eastern, slopes of the Rocky Mountains. Each of them pursues a generally north-east course for some 300 miles, and then turns sharply to the eastward, uniting some 300 miles eastward of the mountains, where the Plains melt into the Prairies. Between these two rivers and the eastern base of the mountains lies an irregular delta or triangle, which seems susceptible of irrigation at a smaller cost than the residue. The location of Union Colony may be taken as a fair illustration of the process, and the facilities therefor afforded by nature.