THE GLACIAL LAKE AGASSIZ 



By Warren Upham, D.Sc, 



St. Paul, Minn. 



As soon as the departing ire-sheet, which had enveloped 

 the northern United States and British America during the 

 glacial period, in its final melting off the land from south to 

 north, receded beyond the water-shed dividing the basin of 

 the Minnesota River from that of the Red River of the North, 

 a lake, fed by the glacial melting, stood at the foot of the ice- 

 fields, and extended northward as they withdrew along the 

 valleys of the Red River to Lake Winnipeg, filling this valley 

 and its branches to the heights of the lowest points over 

 which an outlet could be found. Until the ice-barrier was 

 melted away on the area now crossed by the Nelson River, 

 thereby gradually draining this glacial lake, its outlet was 

 along the present course of the Minnesota River. At first 

 its overflow was upon the nearly level undulating surface 

 of the drift, 1,050 to 1,125 feet above the sea, at the west 

 side of Traverse and Big Stone counties, Minnesota; but in 

 process of time this cut a channel there, called Brown's 

 Valley, 100 to 150 feet deep and about a mile wide, the highest 

 point of which, on the present water divide between the Missis- 

 sippi and Nelson river basins, is 975 feet above the sea-level. 

 From this outlet the Red River valley plain extends 315 miles 

 north to Lake Winnipeg, which is 710 feet above the sea. 

 Along this entire distance there is a very uniform continuous 

 descent of a little less than one foot per mile. 



The farmers and other residents of this fertile plain are 

 well aware that they live on the area once occupied by a great 

 lake; for its beaches, having the form of smoothly rounded 

 ridges of gravel and sand, a few feet high, with a width of 

 several rods, are observable extending almost horizontally 

 long distances upon each of the slopes which rise east and west 

 of the valley plain. Hundreds of farmers have located their 



