Ch. XX.] 



Fig. 354. 



CORALS OF THE OOLITE. 

 Corals of the Coral Kag. 



303 



Fig. 855. 



Thecosmilia annularis, Milne Edw. and J. Haimfi. 

 Coral rag, Steeple Ashton. 



Thamnasb'cea. 

 Coral rag, Steeple Ashton. 



agaiu recur iiiYorksliire, near Scarboroiigli. The Ostrea gregarea (jSg. 356) 

 is very characteristic of the formation in England and on the continent. 



One of the hmestones of the Jura, referred to the age of the Enghsh 

 coral rag, has been called " Nerinsean limestone" (Calcaire a Nerinees) 

 by M. Thirria ; Nerincea being an extinct genus of univalve shells, much 

 resembhng the Ceritkium in external form. The annexed section (fig. 357) 

 shows the curious form of the hollow part of each whorl, and also the 

 perforation which passes up the middle of the columella. JV. Goodhallii 



Fig. 857. 



Fig. 856. 



Ostrea gregarea. 

 Coral rag, Steeple Ashton. 



2s^erincen Ideroglyplnca. 

 Coral rag. 



Nerincea Goodhallii, 

 Coral rag, "Wey mouth. I : 



(fig. 358) is another Enghsh species of the same genus, from a formation 

 which seems to form a passage from the Kimmeridge clay to the coral 

 rag.* 



A division of the oolite in the Alps, regarded by most geologists as 

 coeval with the English coral rag, has been often named " Calcaire a Di- 

 cerates," or " Diceras limestone," from its containing abuudantly a bivalve 

 shell (see fig. 359) of a genus allied to the Ckama. 



* Fitton, Geo], Trans., Second Series, vol. iv, pi. 23, fig. 12. 



