HISTORY OF THE GLACIAL RIVER WARREN. 253 



international boundary, about 450 feet ; above Winnipeg, about 550 feet ; 

 and above the central part of Lake Winnipeg and the north end of Lake 

 Manitoba, respectively about 750 and 650 feet. 



The highest shore of Lake Agassiz, very distinctly marked by beach ridges 

 and rarely by low eroded cliffs, I have traced with levelling along an extent 

 of about 600 miles in Minnesota, North Dakota, and southern Manitoba ; 

 and Mr. J. B. Tyrrell, of the Canadian Geological Survey, has extended 

 this examination a hundred miles farther northward, along the escarp- 

 ments of Riding and Duck mountains. The mouth of Lake Agassiz at its 

 highest stage was 1,055 feet above the present sea level, and the highest ob- 

 served portion of its shore line, reported by Tyrrell near latitude 52° on the 

 northern part of Duck mountain, has an elevation of about 1,460 feet. 

 Along the distance of 400 miles from the southern end and mouth of Lake 

 Agassiz to the north end of Duck mountain, its highest shore thus ascends 

 400 feet ; and the rate of ascent is somewhat uniformly about one foot per 

 mile through the entire distance. This glacial lake has an outlet 125 to 150 

 feet deep and about one and a half miles wide, called Brown's valley, cross- 

 ing the continental water-shed where lakes Traverse and Big Stone now out- 

 flow respectively to the north and south ; and the glacial river which dis- 

 charged the overflow of Lake Agassiz along this channel and the present 

 course of the Minnesota river has been named the River Warren, in honor 

 of Gen. G. K. Warren, who carefully surveyed the whole extent of the valley 

 and rightly explained its origin. The very extensive delta deposits of gravel 

 and sand brought into Lake Agassiz by the Sheyenne, Pembina, Assiniboine, 

 and other rivers, and the associated lacustrine sediments of fine silt spread 

 farther over the lake bed, will be noticed in a later part of this paper, which 

 relates to the departure of the ice-sheet and its contributions of englacial 

 drift to these deltas. * 



The glacial Lake Souris, occupying the basin of the Souris or Mouse river 

 from the most southern portion of this river's loop in North Dakota to its 

 elbow in Manitoba, where it turns sharply northward and passes through 

 the Tiger hills, outflowed in its earliest stage, as already noted, by the James 

 river to the Missouri ; and later to Lake Agassiz by successively lower out- 

 lets, first along the Sheyenne, and last of all by the way of Lang's valley 

 and the Pembina river. North of the Souris basin, an arm of Lake Souris 

 extended along the Assiniboine from Griswold and Oak Lake to some dis- 

 tance above the mouth of the Qu' Appelle ; and the main body of the lake was 

 deeply indented on the east by the high oval area of Turtle mountain, an 

 outlier of the lignite-bearing Laramie formation, which is well developed on 



* Detailed reports on Lake Agassiz are published \>y the Geological and Natural History Survey 

 of Minnesota, Eighth and Eleventh annual reports, and Final report, vols. I and li ; by the U.S. Geo- 

 logical Survey, Bulletin No. 39 ; and by the Geological and Natural History Survey of Canada. An- 

 nual report, new series, vol. IV, part E. More full descriptions and discussion of this glacial lake, 

 now in preparation, will form a monograph of the U, S. Geol. Survey. 



