60 THE GLACIAL LAKE AGASSIZ. 



between these rivers being 85 feet above the South Saskatchewan, 440 feet 

 above the mouth of the Qu'Appelle, and 1,700 feet above the sea. The 

 inclosing lihiifs are composed mainly of glacial di-ift, with only a few 

 exposures of the underlying Cretaceous rocks. The alluvial bottom land 

 of the Qu'Appelle is generally from a half mile to 1 mile wide, and through 

 it the river flows in a winding course, here and there passing- through.long 

 lakes. Like the similar lakes of the Pembina and Minnesota rivers, these 

 owe their existence to the recent deposits of tributaries, and show that the 

 bed of the glacial river was considerably lower- than that of the present 

 stream. The outflow of the Saskatchewan glacial lake, fed by the melting 

 ice fields of an immense area, reaching west to the Rocky Mountains, took 

 its course east by this trough-like channel or valley, entering the Assini- 

 boine at Fort Ellice and reaching tlie border of Lake Agassiz at Brandon. 



Long or Last Mountain Lake, about 50 miles long from south to north 

 and 1 to 2 miles Avide, lying north of the upper part of the Qu'Appelle 

 and tributary to it, occupies a similar glacial watercourse. The elevation 

 of Long Lake is 1,598 feet, being about 100 feet lower than the divide in 

 the channel from the elbow of the South Saskatchewan to the Qu'Appelle. 

 It seems probable that when the ice-sheet had receded so far north as to 

 allow the Saskatchewan Lake to extend to the district, northwest and north 

 of Long Lake, it there obtained some lower point of discharge and out- 

 flowed along the course of this lake, forsaking its former* outlet."^ Owing 

 to the changes in relative elevation which have taken place in the region of 

 Lake Agassiz since that time, this new outlet, or the earliest and highest 

 one of several successive outlets, across the watershed between the Sas- 

 katchewan basin and Long Lake, may now be found 50 or perhaps even 

 100 feet higher than the old channel to the head of the Qu'Appelle — that 

 is, 1,750 or 1,800 feet above the sea, the possible difference being prob- 

 ably as much as a foot to eacli mile of the distance between the old and 

 new outlets. 



Souris River, flowing circuitously southwestward from Assiniboia into 

 North Dakota and thence northeastward into Manitoba, became tributary 

 to the.Assiniboine after the waters of the glacial lake in its own basin, at 



'Report of the Assiniboine aud SaskatcUewau Exploring Exiiedition, 1859, pp. 28. 35, 118. 



