60 



PHYSIOGRAPHY 



The depth which a valley may reach depends on the height of 

 the land in which it is. The higher the land, the deeper the valley 

 may become. Such valleys as the canyons of the Colorado (Pis. XII 



Fig. 46. The Canyon of the Yellowstone below the Falls. 



National Park. 



Yellowstone 



and XIII, pp. 52 and 53) and the Yellowstone (Fig. 46) are never 

 found in plains, but are characteristic of plateaus and mountains. 

 The depth which a valley may reach depends also on its distance 

 from the sea by the route which the water follows. Thus if a stream 



