1^0(3 THE GLACIAL LAKE AGASSIZ. 



withdrawn more thau 200 miles to the east, past the Cypress Hills and 

 Wood Mountain, before a lower outlet from the Saskatchewan country 

 north of these highlands would be ol)tained by Twelve Mile Lake and 

 over the present continental watershed to Big Muddy Creek, which flows 

 through the northeastern corner of Montana to the Missouri. But only a 

 slight further retreat of the ice was sufficient to give still lower avenues of 

 di'ainage. As soon as the Missouri Coteau was uncovered a glacial lake 

 occupying the ^•alley of the South Saskatchewan, in the vicinity of its 

 elbow, outflowed by the way of Moose Jaw Creek, and through a glacial 

 lake in the upper Souris or Mouse River basin, to the Missouri near Fort 

 Stevenson. Later the outflow from the Lake Saskatchewan may have 

 passed to the Lake Souris by wax of the Wascana River, after flowing 

 through a glacial lake which probably extended from Regina 60 miles to 

 the westward in the upper Qu'Appelle basin. 



Through the whole period of the existence of the Lake Souris, which 

 at first outflowed to the Missouri and afterward to Lake Agassiz, the g-lacial 

 lake in the basin of the South Saskatchewan, doubtless also at last includ- 

 ing the North Saskatchewan, was tributary to it, and the outlet of this 

 Lake Saskatchewan was transferred to lower courses as the border of the 

 ice-sheet receded from southwest to northeast. In the concluding part of 

 this chapter detailed descriptions of these glacial lakes, and of their succes- 

 sive channels of outflow to Lake Ag-assiz, will be presented. 



Lake Agassiz, the largest of all the glacial lakes of North America, 

 occupying the basin of the Red River of the North and Lake Winnipeg, 

 covered extensive tracts of Minnesota and North Dakota, the greater ])art 

 of Mauitoija, and a considerable area of eastern Saskatchewan and south- 

 western Keewatin. The history of this lake, which increased in area as 

 the ice-sheet decreased, forms the central theme of this chapter, succeeded 

 by reviews of the associated glacial lakes of large size, two of which, Ipng 

 in southern Minnesota and in South Dakota, had their brief existence before 

 Lake Agassiz, the others being contemporaneous with this lake and several 

 of them tributary to it. 



British Colidiihid, Athabasca, and the Noiiluvest Territori/. — Light-colored 

 silt deposits, distinctly stratified and of considerable thickness, which seem 



