FOSSILS OF THE OOLITE. 



onsists at first of layers of marl intermixed with sand, then layers 

 f ferru'ginous o'olites, and strata of compact limestone and clays, 

 more or less pure and fitted for the purposes of the fuller, and 

 hence named fullers' earth. The first of these marly deposits joins 

 with the marls of the lias, but is characterized by a new species of 

 gryphse'a (Jig. 85), which is not found in the preceding layers. 



47. Above these deposits 

 are found fissile marls, lime- 

 stone, with ferru'ginous o'olite ; 

 to which succeed earthy de- 

 posits, the great o'olite, which 

 consists of a variable series of 

 coarse shelly limestone (lo- 

 cally called "rag"), alternat- 

 ing with beds of fine soft free- 

 stone, devoid of fossils, and 

 admirably adapted for building 

 purposes. Above these again 

 come marls, sands, clays, and 

 limestones, some of which are 

 full of shells. They are known 

 under the names of Bradford 

 clay, Forest mar6/e,and Corn- 

 brash. In spite of the num- 

 ber of fossils, often broken and 

 in the state of moulds, found 

 in this group, it is difficult to 

 designate those which are cer- 

 tainly characteristic of it. Fig. SS.Grypha'a cym'bium. 



48. To the Gryphse'a cym'bium (Jig. 85), which is characteristic 

 of the first group of the o'olitic deposit, and forming, as it were, a 

 Obwgeognostic horizon, we may add the O'strea acumina'ta (./zg.86), 



Terebra'tula digona 



Fig. 86. O'strea acumina'ta. 



47 What is found above the lovver o'olite ? 

 26* 



