268 



OUR COMMON BRITISH FOSSILS. 



brush to laboriously wash away the chalk matrix, 

 will bring the collector off triumphantly. Ostvea ves- 

 cicularis is a very abundant fossil in the Upper Chalk. 

 It is found in every stage of development, from the 



young spat no bigger than 

 a pin's head, to a grotesque 

 and many-layered old 

 Ostrea. One learns a good 

 deal of the conditions of 

 the deep sea-bed where 

 chalk was formed, from 

 such fossils as O. vescicu- 

 laris, I know of no other 

 fossil so apt to bewilder 

 the young geologist, for 



Fig. 2iT—Pecten inequvisival f ts CXtcmal shapCS arC 



(Greensand). 



various. The fact is, it 

 could find few or no solid objects amid the slimy, 



f^orrte 



Fig. 2A,^.—Pecten asper (Greensand). 



