32 THE ORIGIN OF SOILS [chap. 



Under certain conditions the salts are brought to the 

 surface and there effloresce (alkaline soils). These 

 soils occur in the Western States of America (Utah, 

 Arizona, etc.), Australia, South America, Asia (Siberia, 

 Mesopotamia), parts of Spain, etc. 



4. Black soils (Tchernozem) found on the grassy 

 steppes or prairies of the temperate zone, where a 

 continental climate exists with sharp contrasts between 

 winter and summer and a light rainfall of 15-20 inches, 

 occurring mostly in summer. Under these conditions 

 the soils are fine grained, deep, often wind-borne, with 

 a high proportion of carbonate of lime ; but most of all 

 they are characterised by their abundance of humus, 

 not only in the surface layer but at all depths to which 

 the soil persists. Such black soils are found in the 

 Middle West (Manitoba, Iowa, Nebraska, etc.), in 

 European Russia, Hungary and Western Siberia, and 

 in Argentina. They possess an immense reserve of 

 fertility and constitute the chief wheat-producing soils 

 of the world. 



5. Grey soils of the forest zone, formed under some- 

 what similar conditions to the black soils, but where a 

 greater rainfall induces a natural growth of forests 

 instead of grass. These soils contain less humus than 

 the black soils and are also poorer in lime and potash, 

 on account of the greater bleaching to which they 

 have been subject, whereby also their colour becomes 

 lighter and duller. In the main the soils of the United 

 Kingdom, Western Europe, the Eastern States of 

 America and Canada, and the general farming soils of 

 Australia and New Zealand belong to this group, 

 though some fall into the next group. 



6. Peat or ashy soils which originate in cold and 

 cold temperate regions with a high rainfall, generally 

 from glacial deposits. Under these conditions acid 



