314 



OOLITIC GROUP 



[Ch. XX. 



Pteropliyllum comptum. Syn. Cycadites comptus. 

 Upper sandstone and shale, Gristhorpe, near Scarborough. 



Fig. 385. 



Hemitelites JBrownii, Goepp. 

 Syn. Phlehopteris contigua, Lind. & Hutt. 



CTppcr carbonaceous strata, Lower Oolite, Gristhorpe, Yorkshire. 



Fig. 386. 



At Brora, in Sutherlandsliire, a coal formation, probably coeval with 

 the above, or belonging to some of the lower divisions of the Oolitic 

 period, has been mined extensively for a century or more. It affords the 

 thickest stratum of pure vegetable matter hitherto detected in any sec- 

 ondary rock in England. One seam of coal of good quality has been 

 worked 3 J feet thick, and there are several feet more of pyritous coal 

 resting upon it. 



Fuller's Earth {h, Tab. p. 291).— Between the Great 

 and Inferior Oolite, near Bath, an argillaceous deposit, 

 called " the fuller's earth," occurs ; but it is wanting in 

 the north of England. It abounds in the small oyster 

 represented in fig. 386. 



Inferior Oolite. — This formation consists of a calcare- 

 ous freestone, usually of small thickness, which sometimes 

 rests upon, or is replaced by, yellow sands, called the sands of the Inferior 

 Oolite. These last, in their turn, repose upon the lias in the south and 

 west of England. Among the characteristic shells of the Inferior Oolite, 

 I may instance Terehratula fimbria (ng. 387), Rhynchonella sjnnosa 

 (fig. 388), and Pholadomya fidicula (fig. 389). The extinct genus 

 Pleurotomaria is also a form very common in this division as well as in 

 the Oolitic system generally. It resembles the Trochus in form, but is 



Ostrea acuminata. 

 Fuller's Earth. 



