OEIGIN OF THE SOIL 



15 



the rocks. The weathering effects of water are not confined 

 to a layer near the surface, as in decomposition by the air, 

 but extend downward as far as the water can penetrate. 



Photograph by H. L. Hollister Land Co. 



FIG. 3. A deep valley in Colorado, excavated mainly by running water 



Not only does the water dissolve the rocks, but it carries 

 the dissolved materials away to be deposited elsewhere when 

 the water evaporates, thus building up in one place what it 

 tears down in another. In this way the stalactites and stalag- 

 mites found in limestone caves are formed, and our beds of 

 rock salt, gypsum, and bog irons are due to the same process. 



