THE WORK OF RUNNING WATER 



55 



forest, carries away little soil, because' the roots of the vegetation 

 help to hold it. Gullies or " washes" often develop in plowed fields 

 which lie on slopes, where other fields which are not tilled do not 

 suffer to the same extent. In some parts of France, all the soil on 

 hill and mountain 

 slopes has been washed 

 away since people be- 

 gan to cultivate the 

 land. Little dams have 

 now been made in 

 some of the ravines 

 and valleys to check 

 the flow of water and 

 the removal of soil 

 (Fig. 43). In the 

 southern part of our 

 own country and else- 

 where, slopes which 

 were once covered with 

 soil have become bar- 

 ren because the soil 

 has been washed away. 

 The water flowing 

 down a slope may flow 

 as a sheet, or it may 

 be gathered into 

 streamlets. It carries 

 more mud, etc., when 

 it is gathered into 

 streamlets, because 

 such water runs faster. It is where the water is gathered into 

 streamlets as it runs down the slope that little gullies are washed 

 out (Fig. 41). 



The stream in the valley not only carries away much of the sedi- 

 ment brought to it by sheet-wash and temporary streamlets, but 

 it gathers more sediment from its bed and banks. This is true, for 

 example, wherever the bed of a stream is composed of loose material, 



Fig. 43. Shows the method of restraining the 

 water of mountain torrents, to prevent the 

 carrying away of the soil. Savoie, France. 

 (Kuss.) 



