12 ROYAL SOCIETY OF CANADA 



As one goes up the valley into the mountains various terraces appear 

 at higher levels, though the highest ones are of morainic materials which 

 cnce filled the valley but have been cut away to different degrees as the 

 liver has lowered its bed. 



As mentioned before, George Dawson was of the opinion that the 

 \vestern plains were below sea level at the end of the Glacial period and 

 that the evidences of water action pointed to the presence of the sea on 

 which icebergs were at work. However, the entire absence of marine 

 fossils, except some foraminifers which may have been derived from the 

 underlying Cretaceous or Laramie, makes Tyrrell's supposition of glacial 

 lakes more probable. It is altogether likely, however, that the south- 

 western part of Alberta stood much lower than now; since the Keewatiu 

 ice sheet, starting from the low Laurentian hills west of Hudson bay, 

 then not more than 1,000 feet above the sea, can hardly be imagined to 

 have climbed the present slope of 3,000 or 4,000 feet to the foot of the 

 mountains 1,000 miles away. 



Conclusions. 



The succession of events m Alberta during Pleistocene times begins 

 with an advance of the CordiReran ice sheet to a distance of more than 

 40 miles from the mountains at Calgary and of 70 miles west of Ed- 

 monton, as shown by the lower boulder clay free from, eastern stones. 

 Since two boulder clays are known from many other places, the eastward 

 edge of the ice may have reached a similar distance out on the plains 

 there also, but no careful study of the origin of the stones in the lower 

 till has been made to prove this. 



The Cordilleran ice then retreated and an interglacial interval 

 ensued, which was followed by glacial lakes ponded in front of the 

 advancing Keewatin ice sheet. 



The interglacial beds deposited by lakes or rivers or as peat bogs 

 were then covered by a later till charged with Archaean stones mixed 

 with those from the Eocky Mountains. When this ice sheet melted, 

 great glacial lakes were formed once more between the ice front and the 

 mountains, spreading silt and clay over much of the region and bearing 

 icebergs and floes which transported and dropped Archaean boulders miles 

 west of the margin of the Keewatin boulder clay. 



The southwestern part of Alberta may then have stood much lower 

 than now, but probably did not reach sea level. 



There is no unglaciated gap between the regions covered by the 

 Cordilleran and Keewatin ice sheets since their respective territories 

 overlapped ; but as they reached their greatest extent at different times the 

 two sheets never coalesced. 



