450 On the Agricultural Geology of England and Wales. 



miles asunder. The lower oolitic group consists, in Gloucester- 

 shire, of calcareous rocks, known as the cornbrash, the forest 

 marble, and the great, or Bath, oolite, associated with beds of 

 clay~the fullers' earth bed and Bradford clay — and some sand. 

 The inferior oolite, which forms the lowest bed of the group, and 

 which is a ferruginous and calcareous rock, with occasionally 

 much siliceous matter, passes in the north of Oxfordshire and in 

 Northamptonshire and Rutland into a broad tract of ferruginous 

 sands and sandstones. In Yorkshire it consists of sandstones and 

 shales resembling those of the coal measures, and containing 

 seams of inferior coal, the cornbrash being the only calcareous 

 member which is constant, and the great oolite being represented 

 by a thin calcareous band. The group is identified with that of 

 Gloucestershire, under all these varying conditions, not only by 

 containing the same group of fossils, but by having been followed 

 continuously along the outcrop, so as to trace the gradual passage 

 from one mineral form to another. 



As another example, we may take the chalk. Through France^ 

 Belgium, Poland, and other parts of the north of Europe, it 

 maintains its well-known English character of a soft and white 

 carbonate of lime. In the south-east of Europe it assumes the 

 form of soft clays and loose sands, not unlike parts of our plastic 

 and London clay series. In America it is almost wholly arena- 

 ceous ; but, under all these varying conditions, it contains the 

 same group of shells, sponges^ and fishes, and holds the same 

 relative position to other assemblages of fossils which are found 

 in England above or below the chalk. 



It is of necessity, therefore, that our geological maps exhibit 

 lirpas occupied by the outcrops of groups containing the same 

 groups of fossils, matter what their mineral character ; but the 

 mine'ral character of the strata, or of their several parts, is of the 

 most importance to agriculture^ If the superficial deposits were 

 removed, as they are supposed to be, and if the soils were derived 

 wholly from the rocks on which they rest, unaffected by aqueous 

 transport and unmixed with other matter, it would be of more 

 consequence to the agriculturist to know whether, in a given dis-> 

 trict, they consist of clay, sand, or limestone, than whether they con- 

 tain certain fishes, reptiles, or mammals, and particular genera and 

 species of shells. These mark the part of the series to which the 

 strata belong, and they mark those minor modifications to which 

 the argillaceous, calcareous, and siliceous strata are respectively 

 subject in different parts of their vertical range; but these are of 

 less importance than the broad argillaceous, calcareous, and 

 siliceous characters belonging to them, which are independent of 

 their place in the series. 



Mineral characters are also of more practical importance than 



