As the object of this work is to place before its readers all the essential information now obtainable concerning the great plains, no apology will be necessary for adding some of the observations and opinions of other competent writers upon the same subject. By far the most valuable source which I have found to draw from in this connection, is the comprehensive report published by Government, and bearing the title of "United States Geological Survey of Wyoming and Contiguous Territory, 1870. Hayden." THE GREAT WEST. Prof. Thomas informs us, in his report (embodied in Hayden's survey), that, lying east of the divide, "the broad belt of country situated between the 99th and 104th meridians, and reaching from the Big Horn Mountains on the north to the Llano Estacado on the south, contains one hundred and fifty thousand square miles. If but one-fifth of it could be brought under culture and made productive, this alone, when fully improved, would add $400,000,000 to the aggregate value of the lands of the nation. And, taking the lowest estimate of the cash value of the crops of 1869 per acre, it would give an addition of more than $200,000,000 per annum to the aggregate value of our products. "One single view from a slightly elevated point often embraces a territory equal to one of the smaller States, taking in at one sweep millions of acres. Eastern Colorado and Eastern Wyoming each contains as much land sufficiently level for cultivation as the entire cultivated area of Egypt." FALL OF THE RIVERS. The fall of the principal rivers traversing the region above named is about as follows: Arkansas, to the 99th meridian, eleven to fifteen feet to the mile; the Canadian, the same; the South Platte, from Denver to North Platte, ten feet to the mile; the North Platte, to Fort Fetterman, seven feet to the mile. The descent of the country from Denver Junction to Fort Hays is nine feet to the mile. Thus it will be seen that abundant fall is obtainable to irrigate all the lands adjacent. THE PRINCIPAL RIVERS AND VALLEYS OF BUFFALO LAND. The Platte (or Nebraska), the Solomon, the Smoky Hill, and the Arkansas, are the four largest rivers of Buffalo Land proper, and form natural avenues to the eastward from the mountains which shut it in upon the west. THE VALLEY OF THE PLATTE.