104 LAKES OF NORTH AMERICA. 



Gen. G. K. Warren, who first explained the origin of the valley now 

 occupied by Lake Traverse, Big Stone lake, and the Minnesota river, l)y 

 showing that it Avas excavated by a stream flowing to the Mississippi 

 from a former lake to the north. This ancient river, whose source has 

 long since been sapped by northward drainage, has been named River 

 Warren, after its discoverer. 



The great lake that formerly flooded the Winnej^eg basin, and during 

 its highest stage overflowed through River Warren, has been named Lake 

 Agassiz, by Warren Upham, in honor of Louis Agassiz. Practically all 

 of the facts and conclusions here presented concerning the history of that 

 remarkable lake, have been made known through the long-continued and 

 skillful investigations of Upham, under the auspices, at different times, 

 of the geological surveys of Minnesota, the United States, and Canada,^ 

 respectively. 



The Red River of the North rises in the western part of Minnesota, 

 and receives the tribute of Lake Traverse, situated on the Minnesota- 

 Dakota boundary, and at the southern limit of the countr}- formerl}- 

 flooded by Lake Agassiz. From Lake Traverse the present drainage is 

 northward through narrow channels sunken in the sediments of the 

 former lake. Between the streams there are broad, nearly level, inter- 

 stream spaces, forming typical examples of new-land areas, on which 

 shallow ponds form during rainy seasons. About the borders of this 

 broad, level extent of prairie land, now transformed into wheat fields, 

 there are gravel ridges which mark the surface level of the former lake at 

 various stages. These ancient beaches have been traced northward and 

 found to diverge toward the northeast and northwest when the central 

 area of the old lake was approached, and have been mapped so as to show 

 approximately the extent of the water body that built them. By patiently 

 following these ancient shore-lines, it has been demonstrated that Lake 

 Agassiz covered a region about 110,000 square miles in area. Its 

 diameter from north to south was 675 miles, and from east to west, in the 

 wider portions, varied from 225 to 300 miles. It was the largest of the 

 Pleistocene lakes of North America thus far discovered, and exceeded the 

 combined areas of the present Laurentian lakes. The rim of its hydro- 

 graphic basin embraced a region not less than half a million square miles in 

 area. At the site of Lake Winnepeg the ancient lake was 600 feet deep. 



^ A report on these investigations appeared in the Geol. and Nat. Hist. Survey of Canada, 

 Ann. Rep., vol. 4, 1888-9, pp. 1-150 E, and a monograph on the same subject is soon to be 

 issued by the U. S. Geol. Survey. 



