THE BLESSING OF ARIDITY 



provinces, the lands referred to in India and China are 

 arid or semi-arid, and, unlike the Nile Valley, they have 

 not been enriched by sedimentry deposits or fertilized 

 by irrigation. 



Hence, Professor Hilgard reaches the somewhat sensa- 

 tional conclusion that the extraordinary fertility which, 

 by world-wide acknowledgment, marks the valley of the 

 Nile, is a quality inherent in aridity itself. And he main- 

 tains his contention thus : 



" Soils are formed from rocks by the physical and 

 chemical agencies commonly comprehended in the term 

 weathering, which includes both their pulverization and 

 chemical decomposition by atmospheric action. Both 

 actions, but more especially the chemical one, continue 

 in the soil itself ; the last named in an accelerated meas- 

 ure, so as to give rise to the farmer's practice of ( fallow- 

 ing' that is, leaving the land exposed to the action of 

 the air in a well-tilled but implanted condition, with a 

 view to increasing the succeeding year's crop by the ad- 

 ditional amount of plant-food rendered available, during 

 the fallow, from the soil itself. 



" This weathering process is accompanied by the 

 formation of new compounds out of the minerals origin- 

 ally composing the rock. Some of these, such as zeolites 

 and clay, are insoluble in water, and therefore remain in 

 the soil, forming a reserve of plant-food that may be 

 drawn upon gradually by plants ; while another portion, 

 containing especially the compounds of the alkalies pot- 

 ash and soda are easily soluble in water. Where the 

 rainfall is abundant these soluble substances are current- 

 ly carried into the country drainage, and through the 

 rivers into the ocean. Among these are potash, lime, 



37 



