GENESIS OF THE SOIL AND ITS POSSIBILITIES 195 



cess of soluble salts could be removed, these lands under 

 favorable conditions of moisture and temperature would 

 produce large crops. 



The formation of the alkali may be briefly described 

 as follows: By the decomposition of the native rocks, 

 certain salts soluble in water are formed. These salts 

 in the present matter are chiefly sodium and potassium 

 sulfates, chlorids and carbonates. The salts of potash 

 together with those of lime are more tenaciously held 

 by the soil than the soluble salts of soda, and the re- 

 sult of this natural affinity of the soil for soluble potash, 

 lime and magnesian salts is seen in the formation at 

 the surface of the earth, by the process of evaporation 

 above described, of a crust of alkaline material which 

 is chiefly composed of the soluble salts of soda. In 

 countries which have a sufficient amount of rainfall, 

 these soluble salts are carried away either by the sur- 

 face drainage or by the percolation of water through 

 the soil, and the sodium chlorid is accumulated in this 

 way in the waters of the ocean. But where a sufficient 

 amount of rain-fall does not occur, these soluble salts 

 carried down by each shower only to a certain depth 

 rise again on the evaporation of the water, reinforced 

 by any additional soluble material which may be found 

 in the soil itself. The three most important ingre- 

 dients of the alkali of the lands referred to are sodium 

 chlorid, sulfate, and carbonate. When the latter salt, 

 namely, sodium carbonate, is present in predominant 

 quantity, it gives rise to what is popularly known as 

 black alkali. This black color is due to the dark col- 

 ored solution which sodium carbonate makes with the 

 organic matters or humus of the soil. The black 

 alkali is far more injurious to growing vegetation than 

 the white alkali composed chiefly of sodium sulfate and 



