] CLASSIFICATION OF SOILS 33 



umus generally forms and brings about the bleaching 

 f the soil particles and the very complete removal of 

 ,11 nutrient materials like lime and potash. When dry 

 hey are poor in humus and that is confined to the 

 urface layer, but in water-logged areas peat accumulates. 

 ?hey pass by insensible stages into 



7. Tundra soils, which are developed in arctic 

 limates with low temperatures and a high rainfall. 



Among our own soils, though they all possess the 

 ^roup characteristic of comparative freedom from the 

 oluble products of weathering, we shall find much 

 greater and more localised variety than characterises 

 uch wide reaching and uniform soils as the loess or 

 he black soils. Although a distinction has been drawn 

 )etween sedentary soils and soils of transport, there 

 Lre few sedentary soils that do not contain material 

 vhich has been carried from some other formation at 

 1 distance ; only on great stretches of flat country 

 Delonging to a single geological formation may be 

 expected a soil purely derived from the rock below. 

 Especially in Britain, where the outcrops of the different 

 brmations are generally narrow, and where the surface 

 is always undulating, we find that the continual creeping 

 3f soil particles to lower levels has resulted in an 

 admixture of foreign material in most soils. " La 

 :ouche tres mince de la terre vegetale est un monument 

 d'une haute antiquite " (Elie de Beaumont), so that in 

 many places the soil contains the debris of formations 

 now removed by denudation. In the south-east of 

 England the soils that rest on the chalk, which may be 

 only from a few inches to a few feet below, contain 

 abundance of quartz sand, even up to 75 per cent. 

 No such sand exists in the chalk itself, so that it has 

 come from the lower tertiary beds which once over- 

 spread the chalk. On the wide flats of Weald Clay 



D 



