350 



A. E. CAMERON 



differential elevation of the land following the retreat of the ice 

 front. 



In the second stage (Fig. 12) the water level stood at about 

 1,100 feet. The Hay River ice had retreated to the morainal 

 ridge north of Buffalo Lake and the Peace and Athabaska lobes 

 had similarly retreated. Drainage down the Mackenzie was 



Fig. 12. — Outline map showing probable position of Keewatin ice sheet and lake 

 expansions when the water stood at about the 1,100 foot level. 



still blocked, the lake basins were all continuous, and outlet must 

 have been by way of Fond du Lac on Athabaska Lake, in the long, 

 extended arm of that lake, and thus eastward, probably by way 

 of Churchill River. 



The Mackenzie River outlet must have been cleared soon after, 

 but was apparently blocked farther north, for we find the water 

 level standing at 800 feet and developing beaches on all sides of 



