RIVER DEVELOPMENT 333 



and tortuous course, and the Niagara River, with its lakes 

 and falls, are examples of young rivers. 



Where the slope of the newly exposed surface is consid- 

 erable, the streams flow much more rapidly and develop 

 their courses more quickly. The small irregularities are 

 sooner straightened and the trough Deepened, thus form- 

 ing side slopes down which run little rivulets which in 



YELLOWSTONE RIVER. 

 A young river flowing in a deep trough. 



time form side streams. The heads of these, like the 

 heads of the larger streams, are constantly working back 

 into the undissected area. Gradually the side streams 

 develop side streams of their own, and almost the whole 

 surface is covered with a network of streams. 



As the work of erosion goes on and the streams deepen 

 their valleys, only a few imperfectly drained remnants of 

 the former flat surface are left here and there. These lie 

 between the larger streams in places which the side streams 



