ORIGIN OF QU'aPPELLE RIVER. 251 



probably extended from Regina sixty 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 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'Ap- 

 pelle became uncovered, but its lower portion remained enveloped by the 

 ice, the Saskatchewan outflow probably passed to Lake Souris successively 

 by the Moose Jaw creek and the upper Souris, by the Wascana and the 

 Moose Mountain creek, and by 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. 

 At first this river crossed the divide between the River that Turns and the 

 head of the Qu'Appelle, Avhere it eroded a trough-like channel ; 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. 



A noteworthy feature of many of the old water-courses which were outlets 

 of glacial lakes, then carrying a much greater volume of water than now, is 

 the occurrence of long and narrow lakes in such valleys, of which Long lake 

 in Assiniboia, lying on the west side of a high remnant of the eroded Creta- 

 ceous strata called Last mountain, is a conspicuous example. This lake is 

 about fifty miles long from south to north and one to two miles wide. Its 

 southern end is separated from the Qu'Appelle river by alluvial deposits 

 only a few feet above Long lake, which have been brought into the valley 

 since its great glacial river ceased. Similarly the Qu'Appelle valley has 

 been partly refilled by the postglacial deposits of its tributaries, and the 

 present stream in its course through the Fishing lakes flows at a level about 

 sixty feet above the bed of the outlet from the glacial Lake Saskatchewan. 

 The table on page 252, compiled from Hind's Report of the Assiniboine and 

 Saskatchewan Exploring Expedition, brings into view the remarkable topo- 

 graphic features of this valley, and shows the lengths and maximum depths 

 of the lakes through which the river flows. Its elevations are referred to 

 sea level, approximately, by comparison with the Canadian Pacific railway. 



Other rivers which thus flow through lakes produced by postglacial allu- 

 vium in the beds of the outlets of glacial lakes, are the James river, formerly 

 the outlet of Lake Souris; the Pembina river, which, with Lang's valley, 

 afforded a later outlet from Lake Souris, now marked by Pelican, Rock, and 

 Swan lakes, besides several other lakes of small size ; the Minnesota river, 

 with Brown's valley, by which Lake Agassiz outflowed where now lie lakes 

 Traverse and Big Stone and Lac qui Parle ; the St. Croix river and Lake 



XXXVIir— Bull. Geol. Soc. Am., Vol. 2, 1890. 



