LAKE DAKOTA, 267 



Amherst, on the Aberdeen branch of the Great Northern Railway, 1,312 

 feet above the sea. The elevation of the upper portion of the lake beds in 

 the vicinity of Oakes, and the lack of evidence that the lake waves have 

 acted at any g-reater height upon the adjoining- surfaces of undulating- till 

 and morainic hills, lead to the conclusion that the highest shore-line of the 

 north end of Lake Dakota is not mor^e than 1,345 feet above the sea, show- 

 ing that there was only a shallow expanse of water above the plain of 

 lacustrine silt. On the north the depth of the channel of the inflowing 

 James River, eroded apparently before the glacial retreat could permit an 

 eastward outlet into Lake Agassiz, indicates that the surfaces of land and 

 Avater in the James Valley had gained nearly their present relations, Lake 

 Dakota being- already drained away, when the Wild Rice River and the 

 south end of the Red River Valley were uncovered by the recession of 

 the ice-sheet. It is evident, therefore, that the long area of Lake Dakota 

 has experienced only slight differential changes of level, at least in the 

 direction from south to north, since the departure of the ice. The James 

 River Valley is thus strongly contrasted with the northward uplifting that 

 has affected the Red River Valley, as shown by the beaches of Lake 

 Agassiz, the highest of which rises from south to north about 6 inches per 

 mile for 30 or 40 miles at its south end, but a foot or more per mile within 

 40 miles farther north, and, indeed, has an average northward ascent of 

 about 1 foot per mile through an extent of 400 miles along the west side 

 of this lake in North Dakota and Manitoba. 



LAKE SOURIS. 



As Lake Agassiz gradually extended to the north, following the reced- 

 ing ice barrier, it received successively by three outlets the drainage of the 

 glacial lakes of the Saskatchewan and Souris basins. These streams took 

 the course of the Sheyenne, Pembina, and Assiniboine rivers, each bring- 

 ing an extensive delta de]>osit. With the first retreat of the ice from the 

 Missouri Coteau a glacial lake began to exist in the valley of the South 

 Saskatchewan in the vicinity of the elbow, probably outflowing at au early 

 time by the way of Moose Jaw Creek, and through a glacial lake in the 

 upper Souris basin, to the Missouri near B^ort Stevenson. Later the out- 

 flow from the Lake Saskatchewan may have passed to the Lake Souris by 



