This view of the subject affords us a clue whereby to ascertain, with some degree of precision, the aggregate fall of the water, from the head of the Illinois, to the Gulf of Mexico. Agreeably to the surveys of the Great Canal of New York, the elevation of Lake Erie above tide-water is found to be 564 feet. Hence we may assume, in round numbers, 450 feet as the altitude of the head of the Illinois above the ocean. Of the conformation of the valley in other respects, no other ideas can be advanced but such as are suggested by a general view of the topography of the country, and especially of the courses of the principal rivers, as exhibited in the map of the country drained by the Mississippi. We will only add, that the inclined plain constituting the western side of the valley, or, in other words, the great slope down which the Red, Canadian, Arkansa, Konzas, Platte, and other large rivers have their courses, has probably a greater general inclination than any other side of the valley. In forming an estimate of the aggregate descent of this slope, commencing at tide-water, and extending to the base of the Rocky Mountains, Pike allows 8000 feet, which probably exceeds the truth by more than one-half. We would substitute 3000 feet as the aggregate elevation of the base of the mountains above the ocean, and are of opinion, that this amount rather exceeds the truth. This altitude, added to that of James's Peak as before stated, would give for the height of that Peak above the ocean, 11,500 feet; comparing this altitude with that of the "inferior {266} limit of perpetual snow," as estimated by M. De Humboldt for the latitude of 40 degrees, viz. 9846 feet above the ocean, we find the summit of the Peak 1654 feet higher than that elevation; and judging from appearances, this difference of altitude seemed sufficiently well marked by the distance to which the snow extended from the summit downward, upon the sides of the Peak, to authenticate in a good degree the calculation above stated. * * * * * The foregoing report is intended as a civil rather than a military description of the country. For a partial description of its military features, I beg leave to refer to my report of the 12th May, 1818, to Brigadier General T. A. Smith, on file in the War Department. In the performance of topographical duties I have been aided by Lieutenants Graham and Swift, who have rendered essential service in these and other operations. The former of these gentlemen is at present occupied in completing the calculations upon the various astronomical and other observations we took in connexion with our duties; the latter is engaged in delineating the surveys made in behalf of the expedition.