CH. vi] Depth of Soil 97 



one cannot. But it may be taken as a guiding principle 

 that if a good tilth cannot be secured either the soil or 

 the man is at fault and failure is almost certain to 

 follow. 



Again, the soil must be sufficiently deep. Even the 

 best soil would prove infertile if it were spread out too 

 thinly on a rock or a gravel bed, or if it were water- 

 logged to within a few inches of the surface. Most soils 

 are improved by being deepened, but before deciding 

 how to proceed a careful examination has to be made on 

 the spot. The simplest case arises when a thin layer of 

 rock or conglomerated soU parts the surface soil from 

 the subsoil below: sometimes such a layer has been 

 formed in recent times and is known as a pan. So long 

 as this remains it effectually checks plant growth. When 

 it is broken up and removed a greater depth of soil is at 

 once available and plants develop much more readily. 

 An example of this improvement on a large scale is 

 furnished by Cox Heath, Maidstone, once a waste, now 

 a fertile tract^. 



Sometimes, however, the rock is solid and then it 

 obviously cannot be removed. If it lies in regular layers 

 end on to the surface there is the possibility that some 

 of the roots may be able to find a way in between, as 

 happens in the Upper Greensand beds of West Sussex, 

 but if the layers lie horizontally the chance of success is 

 much smaller. The case becomes still more difficult 

 when the soil lies on gravel. The "shrave" of West 

 Sussex, the commons of Hertfordshire, are formed of 

 thin soils lying on gravel which could never be managed 

 satisfactorily in spite of the fact that good farmers have 



1 This and other reclamations are dealt with more fully in the author's 

 Fertility of the Soil, Cambridge University Press. 



R. s. 7 



