228 MAN AND THE GLACIAL PERIOD. 



Mexico. As lie follows down the valley of the Minnesota 

 River, the observant traveller, even now, cannot fail to see in 

 the numerous well-preserved gravel terraces the high- water 

 marks of that stream when flooded with the joint product 

 of the annual precipitation over the vast area to the north, 

 and of the still more enormous quantities set free by the 

 melting of the western part of the great Laurentide Glacier. 



Numerous other deserted water-ways in the north- 

 western part of the valley of the Mississippi have been 

 brought to light in the more recent geological surveys, - 

 both in the United States and in Canada. During a con- 

 siderable portion of the Glacial period the Saskatchewan, 

 the Assiniboine, the Pembina, and the Cheyenne Rivers, 

 whose present drainage is into the Red River of the North, 

 were all turned to the south, and their temporary channels 

 can be distinctly traced by deserted water-courses marked 

 by lines of gravel deposits.* 



In Dakota, Professor J. E. Todd has discovered large 

 deserted channels on the southwestern border of the gla- 

 ciated region near the Missouri River, where evidently 

 streams must have flowed for a long distance in ice-chan- 

 nels when the ice still continued to occupy the valley of 

 the James River. From these channels of ice in which 

 the water was held up to the level of the Missouri Coteau 

 the water debouched directly into channels with sides and 

 bottom of earthy material, which still show every mark of 

 their former occupation by great streams. \ 



In Minnesota, also, there is abundant evidence that 

 while the northeastern part of the valley from Mankato 

 to St. Paul was occupied by ice, the drainage was tempo- 

 rarily turned directly southward across the country through 

 Union Slough and Blue Earth River into the head-waters 

 of the Des Moines River in Iowa. 



* For further particulars, see Ice Age, pp. 293 et seq. 

 f For particulars, see Ice Age, p. 292. 



