308 



STONESFIELD SLATE. 



[Ch. XX 



far the limitation of species to certain minor formations has been due to 

 the local influence of stations, or how far it has been caused by time or 

 the creative and destroying law above alluded to. But we recognize 

 the reality of the last-mentioned influence, when we contrast the whole 

 oolitic series of England with that of parts of the Jura, Alps, and other 

 distant regions, where there is scarcely any lithological resemblance; 

 and yet some of the same fossils remain peculiar in each country to the 

 Upper, Middle, and Lower Oolite formations respectively. . Mr. Thur- 

 man has shown how remarkably this fact holds true in the Bernese 

 Jura, although the argillaceous divisions, so conspicuous in England, are 

 feebly represented there, and some entirely wanting. 



The Bradford clay above alluded to is sometimes 60 feet thick, but, 

 in many places, it is wanting ; and, in others, where there are no lime- 

 stones, it cannot easily be separated from the clays of the overlying 

 " forest marble" and underlying " fuller's earth." 



The calcareous portion of the Great Oolite consists of several shelly 

 limestones, one of which, called the Bath Oolite, is much celebrated as a 

 building-stone. In parts of Gloucestershire, especially near Minchin- 

 hampton, the Great Oolite, says Mr. Lycett, " must have been deposited 

 in a shallow sea, where strong currents prevailed, for there are frequent 

 changes in the mineral character of the deposit, and some beds exhibit 

 false stratification. In others, heaps of broken shells are mingled with 

 pebbles of rocks foreigu to the neighborhood, and with fragments of 

 abraded madrepores, dicotyledonous wood, and crabs' claws. The shelly 

 strata, also, have occasionally suffered denudation, and the removed por- 

 tions have been replaced by clay."* In such shallow-water beds shells of 



Fig. 36S. 



Fig. 36T. 



Fig. 369. 



Terebratida digona. 

 Nat size. Bradford clay. 



Purpuroidea nodulata. Jnat. size. Cylindrites acutus, Sow. 

 Great Oolite, Minchinhampton. Syn. Actmon acutus. 



Great Oolite, Minchinhamptou. 



Fig. 370. 



Patella ruffosa. Sow. 

 Great Oolite. 



Fig. 371. 



Nerita costulata, Desh. Pimida (Emarginula) 

 Great Oolite. clathrata, Sow. Great Oolite. 



* Lycett, GeoL Journ. vol. iv. p. 183. 



