240 tiip:3e strata are often continuous ovkr larue arkas 



red sand-stone, and the coal-measures, lying over each other in their 

 natural positions — the lime-stone uppermost, the sand-stone next, and 

 the coal beneath both. Whenever these three rocks are met with, near 

 each other, they always occupy the same relative position, the coal 

 never appears above this lime-stone, and the sand-stone, if present, is 

 always between the two other series of beds. The same is true of every 

 other group of strata — the order in which they are placed over each othe# 

 is universally the same. 



2°. These beds are generally continuous also over very large areas— 

 or are found to stretch, without interruption, over a great extent of coun- 

 try. Hence when they dip beneath other beds, as they are seen to do 

 in the above diagrams, we can still, with a high degree of probability, 

 infer their presence at a greater or less depth, wherever we observe oa 

 the surface those other beds which are known usually to lie immediate- 

 ly above them. Thus, if in a tract of country consisting of the magne- 

 sian lime-stone (3) above-mentioned, it is known that deep vallies occur, 

 it becomes probable that the soil in those vallies will rest upon, and may 

 be formed from, the underlying red sand-stones or coal-measures ; and 

 that it will therefore possess very different agricultural capabilities from 

 the soil that generally prevails around it. Or in chalk districts, beneath 

 which usually lies the green-sand, the presence of a deep valley cutting 

 through the chalk almost necessarily implies in the hollow a very differ- 

 ent soil from that which' is cultivated in the chalk wolds above. This is 

 the case in the valley of Kingsclere, where the peculiar wheat soil oc- 

 curs, of which an approximate analysis has been given in page 234. 



3°. It has been already stated that the stratified rocks, though so very 

 numerous and so varied in appearance, yet consist generally of repeated 

 alternations of lime-stones, sand-stones, and clays, or of mixtures of two 

 or more of these earthy substances. But the several series of strata are 

 nevertheless distinguished from each other by peculiar and often well- 

 marked characters. 



Thus some are soft, crumble readily, and soon form a soil, — while 

 others, though consisting of the same ingredients, long refuse to break 

 into minute fragments, and thus condemn the surface of the country 

 where they occur to more or less partial barrenness. 



In others, again, the proportions of sand or lime are so varied, from 

 bed to bed, that the character of the mixture in each is entirely different 

 - — so that while one, on crumbling down, will give a stiff clay, another 

 will produce a loam, and a third a sandy marl. 



Or, in some rocks the remains of vegetables are present in considera- 

 ble quantity, — as in the neighbourhood of our coal-beds — or the bones or 

 shells of animals in greater or less abundance, by each of which the 

 agricultural characters and capabilities of the soils formed from them, 

 will be more or less extensively affected. 



Or lastly, the mixture of other earthy substances gives a peculiar 



