274 THE GLACIAL LAKE AGASSIZ. 



could, by a vision of tlie past, see in detail all the successive glacial lakes 

 of Alberta, Saskatchewan, and Assiniboia, and the old rivers flowing from 

 them over the present watersheds, there would surely be revealed a very- 

 complex history, wliich future glacialists can hope to discover only by 

 much patient exploration. 



GLACIAL LAKES OF THE PEACE AND ATHABASCA BASINS. 



In the preceding chapter I have shown that the ice-sheet probably 

 stretched as one continuous mer de glace from the Atlantic to the Pacific, 

 wholly covering the Rocky Mountains in then* low portion adjoining the 

 Peace River. Its thickness there may have been 3,000 to 5,000 feet, 

 and from this central part its surface sloped downward both to the south 

 and north. During the departure of the ice, therefore, its southern border 

 in this region, as elsewhere along its entire extent across the continent, 

 retreated in general toward the north, with embayments here and there 

 between projecting ice-lobes. Thus there came a time when the Peace 

 River basin had become mostly or wholly uncovered from its icy mantle, 

 and held a lake shut in on the north by the receding glacial barrier. West 

 of the one hundred and seventeenth meridian, according to Dr. Gr. M. Daw- 

 son, the elevated plains which are intersected by the deep valleys of the 

 Peace and Smok}^ rivers and their tributaries are overspread by fine lacus- 

 trine silts lying on the glacial drift.^ The elevation of this silt-enveloped 

 country ranges from 2,000 to 2,500 feet above the sea, and it may be 

 merely a vast delta occupying but a small part of the fully expanded 

 Peace Lake. 



The earliest outlet from this glacial lake probably flowed across the 

 present watershed between the Peace River and Lesser Slave Lake, which 

 is about 2,430 feet above the sea; and then, after j)assing tln-ough a smaller 

 glacial lake, or confluent part of the Peace Lake, in the upper Athabasca 

 basin, it may have passed across the divide between the Tow-ti-now River 

 and the North Saskatchewan, on or near the trail from Athabasca Landing 

 to Edmonton. The height of this watershed is about 2,485 feet. Later 

 stages of the glacial retreat would give successively lower outlets, until the 



' Ceol. and Nat. Hist. Survey of Canada, Report of Progress for 1879-80, p. 142 B ; Trans., Eoyal 

 Society of Canada, Vol. VIH, sec. 4, 1890, p. 47. 



