Characters of Sandy Soils 89 



It is also frequently poor in nutritive salts. In a very- 

 dry climate such a soil is particularly unfavourable to 

 vegetation because it cannot form humus. In a climate 

 with a considerable rainfall the surface-layers of soil tend 

 to be very poor in soluble nutritive salts because these 

 salts are washed out by the percolation of rainwater. 

 Owing to the deficiency in lime and other bases such 

 soils tend to form and accumulate acid humus which 

 immediately aifects the vegetation, as we shall see in the 

 sequel. Under certain circumstances however, when there 

 is a high level of well aerated ground-water and a fair 

 proportion of soluble salts, mild humus is formed and the 

 soil may be very fertile, as in the case of many alluvial 

 sands, which form good meadowland, and are excellent 

 for certain kinds of cultivation. 



The more recent (Secondary, Tertiary and post- 

 Tertiary) coarse-grained sands and sand- 

 Distribution stones occur almost exclusively in the 

 sands and southern and eastern parts of England and 



sandstones. in the Midlands. Some of the more ex- 

 tensive and characteristic examples are the 

 Bunter Sandstone of the Trias (Midlands), the Lower 

 Greensand (Cretaceous) in the eastern Midlands and 

 south-east, the Ashdown Sand belonging to the Wealden 

 series, the Bagshot and other Eocene sands of the London 

 and Hampshire basins, the Pliocene " Crag " of East 

 Anglia, and various "valley" and "plateau gravels" 

 deposited at intervals during post-Tertiary times, and 

 resting on different older rooks. 



The most generally characteristic feature of the vege- 

 tation of these newer sands and sandstones 

 woodland ■'^ *^® prevalence of heathland. On some of 



them indeed {e.g. the Bast Anglian sands) 

 no woodland which has really good claims to be con- 

 sidered natural has yet been recognised, and it may be 

 that CaZZttTCa-heath and grass-heath (heath pasture) is 



