sag Expedition to the 



than either. But the difFerence of inclination in these plains, 

 is manifest, not only from the comparative velocities of the 

 several streams alluded to, but from the circumstance, that the 

 Illinois is destitute of any considerable rapids throughout its 

 whole course, whereas the Mississippi, in addition to a cur- 

 rent uniformly more rapid, is hurried down the De IVIoyen 

 rapids, eleven miles in length, and the Missouri, without a 

 perversion of terms, may be denominated a rapid, throughout 

 the distance above specified. By a similar course of reason- 

 ing, it may also be made to appear, that the assumed point 

 of intersection on the Illinois is less elevated than any other 

 point, in the same parallel of latitude between that river and 

 Lake Erie, and even that it is somewhat lower than the sur- 

 face of the lake itself, for the aggregate descent from the 

 surface of Lake Michigan, to the point under consideration, 

 is evidently greater than from the surface of the same lake, 

 to that of Lake Erie, or in other words, the descent of the 

 Des Plains from Chicago to its confluence with the Kanka- 

 kee, is greater by a few feet, than that of the stream uniting 

 Lakes Huron and Erie. 



This view of the subject affords us a clue* whereby to as- 

 certain, with some degree of precision, the aggregate fall of 

 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 five hundred and sixty-four feet. Hence we may as- 

 sume, in round numbers, four hundred and fifty 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 especi- 

 ally of the courses of the principal rivers, as exhibited in the 

 map of the country droned 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 in- 

 clination, 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 Moun- 

 tains, Pike allows eight thousand feet, which probably ex- 

 ceeds the truth more than one half. We would substitute 

 three thousand feet as the aggregate elevation of the base of 

 the mountains above the Ocean, and are of the opinion that 



