EFFECTS OF THE MOVEMENTS OF WATER 27 



by heavy rains, rushing down the sides of hills and moun- 

 tains, tumbling the boulders along as they go. You can 

 see the waves of lakes and oceans, beating against their 

 shores, and grinding rock into finer and finer material. 

 After a storm, you have seen the washouts along the 

 roadsides, and the gullies that are cut back into the fields 

 and hillsides (see Fig. 3). You can see, too, that men have 



FIG. 4. View showing how the roots of plants hold the soil and prevent 

 it from being washed away by the rainfall. 



done much work to keep the streams in their courses, and 

 to prevent washouts. 



Here are two very simple facts. Water runs down-hill, 

 and as it runs, it carries things with it. It is just these sun- 

 pie facts that have determined the forms of the land. 

 Water running down-hill is the great sculptor of nature. 

 Slowly but surely the whole surface of the land is being 

 brought down to sea-level. Of course it is a very uneven 

 process; erosion is much more rapid at some places than at 

 others, but it goes on all the time. Where slopes are steep, 



