332 



FIRST YEAR SCIENCE 



in considering the earth's history. If they had, the falls 

 and rapids would have been worn back and smoothed out. 

 Thus, falls and rapids are characteristic of young rivers. 



158. River Development. The rain which falls upon a 

 flat country runs off very slowly, a large part of it soak- 

 ing into the ground. Pools and lakes are formed in the in- 

 closed basins, and sluggish streams with irregular little 

 crooks, which show that the streams have hardly decided 



NIAGARA FALLS. 

 A young river cutting down a layer of hard rock. 



where they want to go, wander in the slight depressions 

 down the gentle slopes and unite with other streams here 

 and there until a river of ever increasing size is formed. 



In some places the streams flow through lakes where 

 they deposit their sediment, thus filling the lake basins. 

 Here and there they pass over hard layers of rock which 

 hold them up in falls and rapids. These they at once 

 begin to smooth down. Rivers of this kind may -well be 

 called young, as their life work is just beginning. The 

 Red River of the North, with its shallow narrow valley 



