FALLEN RAIN. 



71 



When rain falls over mountains which have so been 

 deprived of their natural protection it is no loug'er 

 caught and held back b\' the trees and the forest 

 floor. The roots, which were once the strongest 

 means of binding the soil together, now are gone and 

 leave it without protection against the rushing water. 

 Heavv rains or sudden thaws swell the streams with 



Fig. 46.— Masonry dams built to control a torrent. Students of the French 

 forest school at the right. Alps of southern France. 



marvelous quickness, and give them a wonderful power 

 to cut away their banks. Where the waterway is very 

 steep such a flood often carries with it many times its 

 own weight of earth and stones. As it nears the val- 

 ley it breaks from its bed and makes new channels, or 

 spreads over the lowlands. The current loses its swift- 

 ness, and its load of stones and sterile earth sinks to 



