RIVER DEVELOPMENT 



179 



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 



YELLOWSTONE RIVER 

 A river flowing in a deep narrow trough. 



between the larger streams in places which the side streams 

 have not as yet been able to reach. Almost the entire 

 surface is so intricately carved into drainage lines that 

 wherever water falls it immediately finds a downward slop- 

 ing surface. The main stream by this time has probably 

 smoothed out most of its falls and rapids and has developed 

 long, smooth stretches. 



