32 



F. W. SAKDESON SAIKT AKTHONY FALLS 



and is a veritable gorge, onl}- a fourth of a mile wide, over 100 feet deep, 

 its steep talus-covered sides crowding the river. This relation is shown 

 in figure 2. • 



For several miles in each direction from their junction these valleys are 

 cut into the same geologic formations. The features in which the valleys 

 are alike are therefore referable to influence of the ground rock forma- 



FiGURE 2. — Map of the Minnesota and Mississippi Rivers near their Confluence 



Showing the relation of old and new valleys and of the upper and lower scarps bounding 



the terraces of the rivers 



tions, while the contrasting differences are due to other causes, namely, to 

 the different streams which made the valleys. 



It has been heretofore supposed that the large, broad ]\Iinnesota- 

 Mississippi valley is an "old" vallej-, in contrast to the gorge of the Mis- 

 sissippi, which is a "young" valley. The walls of the latter are fresh or 

 talus-covered only, while the walls of the former have been described as 



