216 THE GLACIAL LAKE AGASSIZ. 



hj Dr. Robert Bell.^ If this belonged to the time of the Carapbell or 

 McCauleyville beaches, as seems most probable, the extent of the lake dur- 

 ing these later stages of southward outflow was even greater than I have 

 supposed it to be at the time of the Herman and Norcross beaches, and the 

 area occupied by Lake Ag-assiz in its numerous stages much exceeded 

 that of my map and estimate. 



Measm'ed on the maps of this report, the portion of Lake Agassiz 

 comprised within the limits of Minnesota has an area of approximately 

 15,000 square miles, and its portion in North Dakota is 6,800 square miles, 

 very neai-ly, making together a tract of about 21,800 square miles in the 

 United States, probably all uncovered from the ice and occupied by the lake 

 during the time of formation of the Herman series of beaches. Within 

 the limits of Manitoba and adjacent parts of Saskatchewan and Keewatin 

 the extent attained by Lake Agassiz during its Hennan and Norcross stages 

 was probably at least 65,000 square miles. Somewhat more than tlu-ee- 

 quarters of its expanse then was north of the international boundary, for 

 while the lake expanded northward with the recession of the ice-sheet, the 

 southern part of the basin was being uplifted and the lake was slowly cut- 

 ting down its outlet, so that it had ah*eady relinquished the margins of its 

 earliest, area in Minnesota and North Dakota. 



During the stages of the lake represented by the Tintah, Campbell, 

 and McCauleyville beaches, probably its area occupied by water at one 

 time gi-ew to exceed 100,000 square miles. Its southern portion, however, 

 was meanwhile diminishing, until at that late time of maximum size of 

 Lake Agassiz not more than a tenth or perhaps a fifteenth part of its 

 water surface was in the United States. The decrease was in width, not 

 in length, for at its maximum stage the outflow was doubtless still to the 

 south by the River Warren. 



REDUCTION TO THE PRESENT GREAT LAKES OF MANITOBA. 



By the melting away of the ice-sheet from the countr}^ northeast of 

 Lake Agassiz this glacial lake at length (detained successive outlets lower 

 than that through Lakes Traverse and Big Stone and tlie Minnesota River. 

 Owing to the northeastward depression of the ice-laden area, the earliest of 



' Bulletin, G. S. A., Vol. I, pp. 303, 306. 



