272 THE GLACIAL LAKE AGASSIZ. 



east- to- west range of the Tiger Hills and the north- to-south range of 

 the Brandon Hills. With the withdrawal of the ice front across the Assini- 

 boine this gap through the moraine was soon channeled deeper, and the 

 Soui'is turned northward at its elbow, leaving its old channel of Langs 

 Valley and flowing with more rapid descent to the Assiniboine in its pres- 

 ent course. The gap has been since eroded to a total depth of 350 feet; 

 and thence northward the Souris has cut a channel about 140 feet deep, 

 chiefly in till, which forms steep bluff's that in many places are now being 

 undermined by the stream. Erosion along this part of the Sotuds is still 

 proceeding rapidly, and the valley has a very new appearance. 



LAKE SASKATCHEWAN. 



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

 first outflowed to the Missouri and afterward to Lake Agassiz, the glacial 

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

 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. When the upper part of the 

 Qu'Appelle became vincovered, but its lower portion remained enveloped 

 by the ice, the Saskatchewan outflow probably passed to Lake Souris suc- 

 cessively by the Moose Jaw Creek and the upper Souris, by the Wascana 

 and the Moose Mountain Creek, and b}- the Summerberry and Pipestone 

 creeks. Finally the whole length of the Qu'Appelle was uncovered, and 

 the great glacial river from Lake Saskatchewan flowed along the course of 

 this valley, which is similar to that of the Pembina in its width and depth 

 and the numerous lakes along its bottom. At first this river crossed the 

 divide between the River that Turns and the head of the Qu'Appelle, 

 where it eroded a trough-like channel like that of Browns and Langs 

 valleys; but later it probably found a lower outlet .farther north, flowing 

 southward to the Qu'Appelle through the valley of Long or Last Mountain 

 Lake. 



The following table, compiled from Hind's report of the Assiniboine 

 and Saskatchewan exploring expedition, l^rings into view the remarkable 

 topogra])hic features of the Qu'Appelle Valley, and shows the lengths and 



