220 THE ICE AGE IN NORTH AMERICA. 



prevented the waters finding their way northward as before ; 

 and, since glacial times, the rainfall of the district has never 

 been sufficiently great, in proportion to the evaporation, to 

 enable the streams to cut through the barrier thus formed. 

 The existence of these old valleys, and the arrangement of the 

 drift deposits with regard to them, throw important light on 

 the former history of the plains. 



Northward, the coteau ceases to be identified with the Ter- 

 tiary plateau, and rests on a slope of cretaceous rocks. It can 

 be followed by Palliser's and Hector's descriptions of the coun- 

 try to the elbow of the South Saskatchewan, and thence in a 

 line nearly due north through the Eagle and Thickwood Hills ; 

 beyond the North Saskatchewan, however, it appears to be- 

 come more broken and less definite. In Dr. Hector's descrip- 

 tion of certain great valleys without outlet in this northern 

 region, I believe I can recognize there, too, the existence of 

 old blonked-up river-courses similar to those just described. 



South of the forty-ninth parallel the continuation of the 

 belt of drift material can also be traced. It runs southeast- 

 ward, characterizing the high ground between the tributaries 

 of the Missouri and the Red River, which has already been 

 noticed in connection with the water-shed of the continent ; 

 but, wanting the backing of the lignite Tertiary plateau, it 

 appears to become more diffuse, and spread more widely over 

 the country. That the drift deposits do not form the high 

 ground of the water-shed, but are merely piled upon it, is evi- 

 dent, as cretaceous rocks are frequently seen in its neighbor- 

 hood at no great depth. . . . 



In the coteau, then, we have a natural feature of the first 

 magnitude— a mass of glacial debris and traveled blocks with 

 an average breadth of perhaps thirty to forty miles, and ex- 

 tending diagonally across the central region of the continent 

 for a distance of about eight hundred miles.* 



To one familiar with the literature of the subject, it 

 would seem that Dr. Dawson's sagacity in thus early dis- 



* " Quarterly Journal of the Geological Society," vol. xxxi (November, 

 1875), pp. 614-616. The facts are more fully stated in his governmental "Re- 

 port on the Forty-ninth Parallel." 



