Deserts 



water, though it may be at great depths below the sur- 

 face. The only real guide to the existence or absence 

 of water is the character of the plant-world. The study 

 of plant associations will assuredly lead to a definite 

 knowledge of the capacities of an unknown and desert 

 country when, that is to say, a sufficiently definite and 

 practical classification of those associations has been 

 attained. 



The desert of Egypt, which, thanks to our own energy 

 and enterprise, is now being made valuable agricultural 

 land, seems to have been once a land of marshes and 

 lagoons, where primitive Egyptians lived, like the hunting 

 and fishing tribes of the Sudd region. The silt of the 

 Nile has filled up those lagoons to such a level that it is 

 only by irrigation that they can be forced to bear a 

 harvest. 



In other places, also, it is quite clear that it is man 

 himself and his attendant animals (vegetable fiends like 

 the goat, the camel, and the ass) that have destroyed the 

 natural vegetation and turned what were once forest- 

 clad hillsides and well-watered slopes into glaring stony 

 hills and arid sandy plains. 



One cannot conclude, therefore, that the world is dry- 

 ing up from such facts as the deposition of silt which 

 has made dry alluvium of what was once a lagoon 

 country, nor from the desiccation due to the destruction 

 of forests, and the havoc of the goat, camel, and ass. 



But every sort of desert is always being invaded by 

 vegetation. 



A country so dry as to be absolutely destitute of 

 plants is exceedingly unusual. In most deserts, scanty, 

 scattered little plants of the most miserable character 

 manage, somehow, to exist in spite of fierce sunshine 

 by day and severe cold at night, not to speak of the 

 friction of the gritty dust carried by gales blowing with- 



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