THE DESERTS OF WESTERN EGYPT 



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but to wind-action. Plants are found in innumerable places in 

 which the supply is no greater than that of the bare areas, but in 

 exposed places the surface layers of sand and gravel are shifted 

 about, exercising a corrosive action that is destructive to plants 

 and highly important in determining the contours of the hills and 

 surface of the rocks. Highly specialized desert species might 

 survive the aridity, but the shifting substratum does not permit 

 them to attain maturity, a condition which would affect both the 

 tender rapidly developing annual and the slowly growing leathery 

 xerophytes. 



