OUTLET BY THE ElYER WAEREN. 15 



banner of the receding ice-sheet caused this glacial lake to fill the Red 

 River Valley and to reach northward, as tlie ice front retreated, over the 

 region of Lakes "Winnipeg, Manitoba, and Winuipegosis, until the continued 

 melting of the ice at last permitted it to be di-aiued by the natural slope of 

 the land to the northeast, excepting its remnants, Avhich form these lakes of 

 Manitoba. 



OUTLET. BED. AND SHORES OF LAKE AGASSIZ. 



RIVER WARREN. 



The lowest point of the watershed dividing the great areas that are 

 di-ained respectively to Hudson Bay and the Gulf of Mexico is between 

 Lakes Traverse and Big Stone, on the boundary line of ]\Iinnesota and 

 South Dakota. Its elevation above the ocean is 975 feet. Here an ancient 

 watercom'se, called Browns ^"alley (see the frontispiece and PI. IV), 

 which was occupied by the River Warren, outflowing from Lake Agassiz, 

 is eroded in the thick sheet of glacial drift to a depth of 100 to 12o feet, 

 with a width of about li miles. The tops of its inclosing blufts and the 

 general level of the adjoining country of undulating or moderately rolling- 

 till ai-e about 1,100 feet al)ove the sea. Portions of this channel contain 

 the long and narrow Lakes Traverse and Big- Stone, the former outflowing 

 by the Bois des Sioux River and the Red River of the North to Lake 

 Winnipeg and Hudson Bav, and the latter bv the ^linnesota River to the 

 Mississippi. But this channel shows that subsequent to the deposition of 

 the drift a great river has flowed here across what is now one of the 

 princijjal watersheds of the continent. 



The head stream of the ]\Iinnesota^ River, from which the State of 

 Minnesota receives its name, after flowing eastward about 20 miles from its 

 sources on the Coteau des Prairies, turns southerly at Browns Valley and 

 enters the noi-thwest end of Big Stone Lake. Here, and in its whole 

 extent thence to its mouth, the Minnesota River occupies the channel of the 

 glacial River Warren. This valley or channel begins at the northern 



'The aboriginal Dakota name, meaning "water nearly clear, but slightly clouded,'' or, poetically 

 translated, "sky-tinted vrater." (A- W. Williamson, in Thirteenth Annual Report. Geol. and Nat. 

 Hist. Survey of Minn., for 1884, p. 109. E. D. Neill, History of Minnesota, 1858, p. xlvii. Nicollet's 

 Report, 1843, p, 69.) 



