How Vegetation Holds the Soil 71 



They carry away the particles of sand and clay which 

 would in time, if there were plant roots to hold them, 

 turn to soil. 



The winds also help keep the desert rocks bare and free 

 of soil. Have you ever been in a dust storm or have you 

 read of caravans caught in such storms in the Sahara 

 Desert? The fierce wind picks up the particles of sand 

 and clay from the bare earth and sweeps them along as it 

 does the snow in winter, or it whirls them in clouds high 

 in the air. The dust clouds are often so dense that they 

 hide the sun and all landmarks by which the traveler can 

 guide his way. But have any of us ever seen the winds 

 pick up much dust from the green fields where the vegeta- 

 tion protects the surface? 



If we turn now to a very wet country, such as that upon 

 our northwest coast, where often nearly eight feet of rain 

 falls in a year, we shall find the vegetation so dense that it 

 hides both soil and rocks. Here water can do little in 



//. W. Fairbanks 



The vegetation prevents the wind from blowing the sand away, so that wherever 

 the roots obtain a hold there a Uttle mound is formed. 



