POST-GLACIAL LAKES IN CANADA 



351 



the present shore line. At the 800-foot elevation (Fig, 13) the 

 ice had receded clear of Athabaska Lake and practically clear of 

 Great Slave Lake, though a small tongue remnant of the Great 

 Slave Lake lobe may have occupied the eastern extension of the 

 lake. The water level was well below the Fond du Lac outlet on 

 Athabaska Lake, but the Mackenzie Valley was open and drainage 



Fig. 13. — -Outline map showing probable position of Keewatin ice sheet and lake 

 expansions when the water stood at about the 800 foot level. 



should have been that way. The two main basins are continuous 

 by means of a narrow strait across the low escarpment at Smith. 

 The Great Slave Lake basin was expanded to take in the present 

 basin of Buffalo Lake, though probably low morainal islands 

 marked the position of the morainal ridge north of Buffalo Lake. 

 On the retreat of the ice, iso static readjustment of the land 

 areas took place, with a raising of the land in a series of differential 



