ix.] ALKALI SOILS 245 



action of the sea water on the texture of the soil, due to 

 the attack of the sodium chloride upon the double 

 silicates of the soil, lime in particular being displaced 

 by soda. The result is the deflocculation of the clay, 

 which will not settle down for many weeks when sus- 

 pended in water. The sodium chloride of the sea water 

 would also interact with any calcium carbonate in the 

 soil, giving rise to sodium carbonate, the deflocculating 

 effect of which upon the clay has already been noticed. 

 Biological effects may also be surmised : it is always 

 seen that the earth worms are killed in the land which 

 has been flooded with sea water, and in view of the 

 known unfavourable effect of chlorides on nitrification, 

 it is possible that the rate of production of nitrates in 

 the inundated soil is seriously lessened. 



Alkali Soils. 



In arid climates the rainfall is often insufficient to 

 produce percolation through the soil and subsoil into the 

 underground water system ; in consequence, the salts 

 produced by the weathering of the rocks tend to 

 accumulate in the subsoil, and may be brought to the 

 surface by capillary rise so as to cause almost entire 

 sterility. Such bad lands are known in America as 

 " alkali soils," but they are well known in India and in 

 Egypt, and indeed are common to all countries possess- 

 ing a small rainfall and great evaporation. In its most 

 aggravated form alkali land, particularly at the end of 

 the dry season, shows an actual white efflorescence of 

 salts at the surface ; all vegetation is destroyed, except 

 one or two plants which seem tolerant of large quantities 

 of saline matter, such as " greasewood," Sarcobatus sp., 

 or the Australian " saltbushes," Atriplex setnibaccatum, 

 etc. In some cases the alkali is chiefly located at a 

 slight depth in the soil, and only effloresces on spots a 



