SUCCESSIVE CHANGES IN LAKE AGASSIZ. 257 



from Lake Agassiz probably crossed the water-slied between the Poplar and 

 Severn ; and later outlets were found along lower courses, including the 

 canoe route by the Hill and Hayes rivers. Each of the successive outlets 

 was probably eroded to a considerable depth, being occupied by the out- 

 flowing river during the time of formation of two or more beaches, until 

 the retreat of the southeastern border of the portion of the ice-sheet remain- 

 ing west of Hudson's bay finally permitted drainage to take the course of 

 the Nelson, the ice-dammed Lake Agassiz being thus changed to Lake 

 Winnipeg. 



Within the time after the ice-sheet had retreated beyond the valley of the 

 lower Saskatchewan, and before its melting upon Hudson's bay permitted 

 Lake Agassiz to gain an outlet northeastward to the sea, it seems certain 

 that the ice must have been melted upon a large region north of the Sas- 

 katchewan basin, where drainage now passes east by the Churchill and 

 north by the Mackenzie, but was then pent up in lakes by the ice-barrier 

 and caused to flow to the south. Lake Agassiz thus received the waters of 

 the upper Churchill, and of the basins of the Athabasca and Peace rivers, 

 the great head streams of the Mackenzie; and the Churchill, and probably 

 also the upper Mackenzie basiu, continued to be tributary to this lake 

 through all its lower stages of outflow to Hudson's bay. 



Extensive areas bordering the Peace river are described by Dr. Dawson 

 as " covered superficially by fine silty deposits resembling those of the Red 

 river valley, and doubtless indicating a former great lake or extension of the 

 sea in the time immediately succeeding the glacial period."* The explora- 

 tion of ancient shore-lines is very difficult in that generally forest-covered 

 region, and it must be many years before the boundaries and outlets of 

 former bodies of water in the basins of the Peace and Athabasca rivers can 

 be mapped ; but it may be predicted with reasonable confidence that these 

 basins, now drained to the Mackenzie and the Arctic ocean, will some time 

 be found to have contained glacial lakes outflowing southeastward to Lake 

 Agassiz. Probably the earliest outlet from the glacial lake of the Peace 

 river was across the water-sheds to Lesser Slave lake and to the North Sas- 

 katchewan at its eastward bend about fifty miles below Edmonton ; and the 

 latest outflow from the Athabasca glacial lake appears to have formed a 

 channel across the continental divide near the famous Methy portage. 



The water-course by which the Churchill, bringing the Athabasca outflow, 

 passed into the Saskatchewan, tributary to Lake Agassiz, extends south- 

 eastward about a hundred miles by Lake of the Woods, Pelican, Heron 

 and Birch lakes, Great and Ridge rivers, Beaver, Sturgeon and Pine Island 

 lakes, to the Saskatchewan at Cumberland house. This was the route 

 of Franklin and Richardson in 1820. The latter states that " by Beaver 



* Descriptive Sketch of the Physical Geography and Geology of the Dominion of Canada, 1884, 

 p. 32. 



