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A. E. CAMERON 



elevations to the north and east, possibly on successive hinge lines. 

 The area south of McMurray was probably differentially raised, 

 causing elevation of the Methy portage outlet, and, later, move- 

 ments developed in the neighborhood of Fort Smith, raising a 

 land barrier there about 125 feet high, and causing a separation 

 of the two basins (Fig. 14). We thus find two large bodies of 



Fig. 14.— Outline map showing probable lake expansion when water stood at the 

 700 foot level. 



water existing in the separated basins: Athabaska Lake, standing 

 at about 750 feet, and Great Slave Lake at some 600 feet. 



The two basins have acted very differently since their separa- 

 tion. Isostatic readjustment north of Athabaska Lake has tended 

 to close the outlet, keeping the waters ponded back, and drainage 

 has been accomplished by Slave River cutting its channel as fast as 

 the ground rose. As a consequence the water level has dropped 



