GEOLOGICAL HISTORY OF THE EARTH 



45 



River of the North and the Minnesota river now have 

 their sources. As the Minnesota river extended west- 

 ward from where it and the Mississippi river came to- 

 gether, it received, during that period, the waters from a 

 very much longer section of the southern edge of the 

 glacier than did the Mississippi river. The watershed 

 of the Minnesota river during that time extended far out 



Figure 7. The dotted surface, including the system of great lakes, and the area 

 marked "Lake Agassiz," shows the area covered by the great glacier during the penod 

 when arctic cold extended far down into the temperate zone. The waters from the melt- 

 ing glacier and from the annual rainfall flowed from the southern arm of Lake Agassiz 

 into the Minnesota river. 



into North Dakota, into the northwest territories of 

 Canada, and even around eastward to the north of the 

 Mississippi river. In other words, " Ancient Lake 

 Agassiz," received water from streams flowing into it 

 from the east and from the west as well as from the 

 surface of the receding glaciers. The larger watershed, 

 supplying a larger flow of water in the Minnesota than 

 was supplied to the Mississippi river during the 

 glacial period, seems to account for the washing out of 



