CH. I 



SOIL 



9 



they are apt to be uprooted by sudden gusts of wind. 

 With more moisture and with or without the help of 

 certain measures, which will be described in another 

 place, other trees and plants are able to establish them- 

 selves and to fix the soil. Thus in the Kordofan 

 Province of the Anglo-Egyptian Sudan long ridges of 

 sand, which had advanced from more rainless and more 



Fig. 3. Acacia tortllis overturned by the wind. 



windy districts, have clothed themselves with open 

 forests of Acacia Verek, which supply the best gum- 

 arabic of commerce. In Southern India the Casuarina 

 equisitifolia has been used successfully in fixing shifting 

 sands on the Madras coast, while in Ceylon the Palmyra 

 palm (Borassus jiabellifer) also gets a hold of sand- 

 dunes in the Northern Province. There are instances 

 where very fine-grained sandy soils, probably cemented 

 by organic matter, are impenetrable to air and water. 



