TRANSPORTED MATERIALS OFTEN MASK THE ROCKS. 267 



generally exists between the soil and the rocks on which it rests, and 

 that the geological structure of a country, as well as the chemical consti- 

 tution of the minerals of which its several rocky masses consist, have a 

 primary and fundamental influence upon the agricultural capabilities of 

 its surface. 



And yet I should be leading you into a serious error, were I to permit 

 you tp suppose that this intimate and direct relation is always to be ob- 

 served — that in whatever district you may happen to be, you will fold 

 the soil taking its general character from the subjacent rocks — and that 

 where the same rocks occur, similar soils are always to be expected. 

 On the contrary, in very many localities the soil is totally different from 

 that which would be produced by the degradation or decomposition of 

 the rocks on which it rests. To infer, therefore, or to predict, that on a 

 given spot, where, according to the geological map, red sand-stone for 

 example prevails, a marly or other red sand-stone soil will necessarily 

 H^ found— or that where the coal measures are observed, poor, ungrate- 

 ful land must exist — would be to form or to state opinions which a visit 

 to the several localitias would in many inistances show to be completely 

 erroneous — and which would bring undeserved discredit upon geologi- 

 cal science. 



In such cases as these geology is not at fault. New conditions only 

 have supervened which render the natural relation between soils and 

 rocks in those places less simple, and consequently more obscure. Yet 

 a further study of geological phenomena removes the obscurity — shows 

 to what cause it is owing that in many districts the soil is such as could 

 never have been formed from the subjacent rocks — again places the en- 

 lightened agriculturist in a condition to pronounce generally from what 

 rocks his soils have been derived — generally also what" their agricultural 

 capabilities are likely to be, and by what mode of treatment those capa- 

 bilities may be most fully developed. 



Of the surface of Great Britain and Ireland it may indeed be truly 

 said, that it exhibits extensive tracts in which the character of the soil is 

 directly influenced by, and may be inferred from, the character and 

 composition of the subjacent rock. To these districts the rules and ob- 

 servations contained in the preceding sections directly and clearly apply. 

 But other extensive tracts also occur in which the character of the soil is 

 independent of that of the rocks on which it immediately rests — the 

 cause of this apparent difficulty we are now to consider. 



1°. I have already had occasion to explain to you in what way all 

 rocks crumble more or less rapidly, and give origin to soils of various 

 kinds. Were the surfaces of rocks uniformly level, and that of every 

 country flat, the crumbled materials would generally remain on the spots 

 where they were formed. But as already shown in the diagrams, in- 

 serted in page 238, the rocks rarely lie in a horizontal position, 

 but rest almost always more or less on their edges ; and the surface in 

 such a country as ours is often mountainous or hilly, and everywhere 

 undulating. Hence the rains ave continually washing off' the finer par- 

 ticles from the higher, and bearing them to the lower grounds — and on 

 occasions of great floods, vast quantities even of heavy materials are 

 borne to great distances, and spread sometimes to a great depth and over 

 a great extent of country — [witness the still recent floods in Morayshire.] 



