220 THE BOOK OF NATURE STUDY 



usually there is a thin, rich, well-drained soil on which a sweet 

 grass grows, forming an excellent pasturage. The different 

 limestones vary considerably in this respect. Usually they are 

 employed for sheep farming, and there are several different breeds 

 with local names, like the Cotswold and the South Downs breeds. 

 The Chalk is a special example of a soft limestone with peculiar 

 features ; the absence of rocky but the presence of steep and 

 dimpled grass slopes, waterless hollows, and steep -sided but 

 grassy combes. The soils are too dry for gardens, but many 

 trees, especially yews and beeches, flourish on them. Heaths and 

 commons occur chiefly where the Chalk is covered with sandy 

 or clayey deposits, so that the influence of the composition of 

 the chalk but not its physical effects are felt. The limestone 

 flora is an extremely rich one, and includes a number of charac- 

 teristic plants, such as the green spleenwort, Anthyllis, Campanula 

 glomerata, Clematis, Helianthernum vulgare, Reseda, some of the 

 orchids, and many other species which only flourish in a 

 calcareous soil. 



Alluvial soils made up of the richest pickings carried from an 

 extensive land surface by river denudation are naturally the 

 richest in plant food and the most fertile in the country. They 

 are suitable for all types of agriculture and for gardens ; their only 

 drawbacks resulting from considerations of flooding and drainage. 



The Glacial Epoch has had an important influence in bringing 

 together the denudation results from all kinds of rocks, and has 

 covered much of the country with material yielding rich mixed 

 soils. Here again the chief drawback results from the clayey 

 nature of the subsoil and the necessity for thorough drainage. 



The chief demands made by mankind upon his environment 

 may be summed up as food, drink, health, wealth, and recreation, 

 and the sites of his dwelling and lines of transport will be found 

 to be largely governed by consideration of these factors. Food 

 was formerly a question mainly of agriculture, but is now chiefly 

 one of transport. Water in villages and isolated places is still 

 related to the immediate environment, although in the larger 

 towns a certain amount of independence has been reached by 

 bringing good water from a distance. Health and wealth are 

 both related in a marked degree to the nature of the earth-crust, 



