THE WORK OF RUNNING WATER. 



93 



on the structure and resistance of the rock. Between these two classes 

 there is no sharp hne of demarkation. Illustrations of two types, 

 dependent largely but by no means wholly on conditions independent 

 of the rock, are cited at this point. Others will be mentioned in other 

 connections. 



Bad-land topography. — To a type of topography developed in 

 early maturity in certain high regions where the rock is but slightly, 



Fig. 75.— Bad-land topography. North of Scott's Bluff, Neb. (Darton, U. S. 



Geol. Surv.) 



though unequally, resistant, a special name is sometimes given. Such 

 regions are termed had lands. Some idea of bad-land topography is 

 gained from Figs. 75 to 78. Bad-land topography is found in various 

 locahties in the West, but especially in western Nebraska and Wyoming, 

 and the western parts of the Dakotas. The formations here are often 

 beds of sandstone or shale, alternating with unindurated beds of clay. 

 Climatic factors are also concerned in the development of bad-land 

 topography. A semi-arid climate, where the precipitation is much 



