CHAPTER II 

 GEOGRAPHICAL DISTRIBUTION 



SOILS containing injurious quantities of alkali are found 

 on every continent. These soils, however, do not occur 

 in all parts of the continents, the distribution being con- 

 fined to areas where conditions favorable to their formation 

 prevail. The most important of these conditions is aridity. 

 Another important factor is the nature of the rock from 

 which the soils were formed. Because these conditions 

 are local, alkali soils are likely to be found over large areas, 

 but all the soils of these areas are not necessarily highly 

 charged with soluble salts. Part of the soils in a region 

 having a climate favorable to alkali formation may be 

 derived from rocks that are low in soluble salts and may 

 have been so deposited that they have good natural drain- 

 age. Soils of this kind do not contain alkali even though 

 most of the soils of the region are impregnated. Likewise, 

 soils high in soluble salts may be found over limited areas 

 in regions where most of the soils are free. This condition 

 is sometimes found in climates that are not entirely arid, 

 or where a soil having poor drainage was derived from 

 rock that was high in soluble salts. Thus, the alkali 

 problem has local as well as general aspects. A general 

 alkali condition may prevail over en extensive region, 

 the smaller areas of which may be exceedingly variable. 



North America. More than half of the North- Ameri- 

 can continent is arid or semi-arid. Throughout this vast 

 area alkali soils are found. There are many large tracts 



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