I J CLASSIFICATION OF SOILS 29 



the subsoil and open it to the access of air and the free 

 penetration of roots, all methods of cultivation should 

 be avoided that would bury the surface soil and bring 

 the subsoil to the top. A plough which inverts the 

 soil should not go below the former limit of cultivation, 

 and if it is desired to deepen this limit, it should be 

 done by degrees, half an inch or so each year. Immense 

 damage has been done to the fertility of many of the 

 heavier soils by rash ploughing with steam, especially 

 where the old " lands " were thrown down, burying the 

 fertile soil in the furrows and baring the raw clay on 

 the tops of the ridges. 



General Classification of Soils. 



Although a distinction has been drawn between 

 sedentary soils and soils of transport, there are few 

 sedentary soils that do not contain material which has 

 been carried from some other formation at a distance ; 

 only on great stretches of flat country belonging 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 formations 

 are generally narrow, and where the surface is always 

 undulating, we find that the continual creeping of soil 

 particles to lower levels has resulted 111 an admixture 

 of foreign material in most soils. " La couche 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- 



