2 4 8 



OUR COMMON BRITISH FOSSILS. 



The Carboniferous formation, in all its divisions, 

 contains plenty of fossil mollusca. In places these 

 are overwhelmingly abundant. The limestone yields 

 several species of Natica. At Castleton, in the Peak 



Fig. 230. Better o^hon hiulcus (Carboniferous limestone). 



of Derbyshire, these fossils are very beautifully pre- 

 served, and often of large size. The largest species, 

 however, is to be met with in the neighbourhood of 



Fig. 231. Posidonia. (Carboniferous). 



Clitheroe, in Lancashire, associated with Bellerophon. 

 Both are met with as solid casts, often besprinkled 

 with small crystals of calcite ; and the geologist will 



