Section IV., 1909 3 ] Trans. R. S. C. 



I. — The Drift of Alberta and the Relations of the Gorâ'dleran and 



Keewatin Ice Sheets. 



By A. P. Coleman. 



(Read May 26th, 1909.) 



Introduction. 



In the complex series of advances and retreats of the great ice 

 sheets which covered almost all Canada and much of the northern United 

 States with boulder clay, the relations of the Cordilleran and Keewatin 

 sheets have remained somewhat in doubt. It is generally accepted that the 

 glaciation of the Eocky Mountains came first, but that the ice sheet 

 resulting from the confluence of the mountain glaciers in the valleys did 

 not advance far over the plains. On the other hand, the later ice sheet 

 advancing from the Keewatin centre is supposed to have halted some 

 distance before reaching the mountains ; so that on maps of the glaciation 

 of North America a belt along the northeastern side of the mountains 

 is left uncovered. 



While it is probably true that the Cordilleran and Keewatin ice 

 sheets never met, this was in reality because of lack of coincidence in 

 time, and not because any strip was left unglaciated between the two: 

 as will be shown later in this paper. In some parts of the region, at 

 least, the boulder clays of the two ice sheets overlap. 



Ever since the late Geoige Dawson studied the geology of the 

 International boundary in 1875, geologists have been familiar with the 

 fact that boulders derived from the Hudson bay region are widely 

 'Scattered over the southern part of the great plains; and the work of 

 McConnell and Tyrrell has proved the same for the ntn'thern part. 

 There has been a difference of opinion, however, as to the agency that 

 spread these erratics, Dawson arguing for marine ice as the cause, at 

 least in the western part of the prairies, while others have laid more 

 stress on the work of land ice spreading in all directions from the 

 Keewatin centre. 



Many large blocks of Archaean rock are found scattered over the 

 foothills in southern Alberta almost to the foot of the Eocky Mountains, 

 at levels from 3,000 to 5,280 feet above the sea. Kow were they raised 

 from the low Archaean hills ],500 feet above Hudson bay to their 

 present levels? Dawson's explanation was that the region of the foot- 

 hills was at that time below sea level so that bergs and floes could 



