EXTENT OF UPPER AND LOWER DRIFT OOO 



condition, yet the absence of any intervening non-glacial beds, or even a 

 distinct line of separation between the looser upper part of the till and 

 the denser lower part, renders one very hesitant to say that more than 

 one stage of glaciation is represented. Where this is the case, it appears 

 to us that the presumption is in favor of reference to deposition by the 

 last ice-sheet traversing the area. 



kelations of the earlier and later drift of the mountain 



Glaciers to that of the Keewatin Ice-sheet 



in southern Alberta 



Doctor Dawson evidently did not think that the mountain glaciers ex- 

 tended beyond the front of the range at a time corresponding to the last 

 continental glaciation in southern Alberta, for, in connection with his 

 discussion of the conditions of deposition of the upper boulder clay which 

 contains northeastern erratics, he states : 12 



"That the glaciers which at the period of the Saskatchewan gravels protruded 

 from the mountains must at this [later] time have shrunk back within the 

 range, in the southern part of the district at least, is shown by the stranding 

 of Laurentian boulders upon the old moraines of these glaciers close up to the 

 foot of the mountains. It is possible that the Bow Valley Glacier may still 

 have continued to hold some importance in the foothill region, but the abundant 

 supply of well rounded gravels, with other circumstances, renders it probable 

 that the Rocky Mountain glaciers generally had become strictly local and 

 relatively insignificant." 



We did not examine the drift of the mountain glaciers west of the limit 

 of continental glaciation in the belt bordering the mountain front north- 

 west of Belly Eiver. From the relations which we observed in the vicinity 

 of the latter stream, however, and farther south, we feel sure that there 

 must have been a similar extension of the mountain glaciers farther north 

 at the Wisconsin stage, and that it was in connection with this extension 

 that the moraines bordering the mountain front were formed. We are 

 inclined to disagree with the interpretation of Dawson when he states 

 that he and McConnell "have found reason to assign to a very early 

 period" the moraines close to the base of the mountains, which 13 are 

 "evidently referable to glaciers of the Rocky Mountains." 



Doctor Dawson states 14 that 



"Mr. McConnell had in 181)0 carefully examined the sections of the glacial 

 deposits along Bow River between the mountains and (Jleichen (about 80 miles 



^G. M. Dawson: Bull. Geol. Soc. Am., vol. 7, pp. <>2-(*»3. 



13 Bull. Geol. Soc. Am., vol. 7, p. 65. 



14 Op. clt., pp. 38 and 39. 



