DIVIDES 175 



down and sweeping away the surface over which it moves. 

 This sort of work is called water erosion. 



When running water is concentrated into a stream, the 

 work of erosion is also concentrated and the wearing down 

 of the stream bed becomes comparatively rapid. This 

 cutting down goes on irregularly, being greatest at time of 

 flood and least when the flow is slight. 



GULLIES BEING CUT BY RUNNING WATER 



Divides. If we carefully observe the drainage of a 

 region, we find that the areas from which different streams 

 gather their water are usually so distinctly separated from 

 one another that a line could be drawn so that wherever 

 water falls the rivulets on one side would flow into one 

 stream and on the other side into another. Such a line of 

 the highest land between the drainage areas of neighboring 

 streams is called a divide. The line may be very distinctly 

 marked, as on mountain ridges, or it may be difficult to 

 determine, as in a flat country, but if the drainage is well 

 established, it will be apparent. 



