268 



OUR COMMON BRITISH FOSSILS. 



brush to laboriously wash away the chalk matrix, 

 will bring the collector off triumphantly. Ostrea 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. 247Pecten inequvisival its external shapCS ai'C 



(Greensand). 



various. The fact is, it 

 could find few or no solid objects amid the slimy, 



Fig. 248. - Pecten asper (Greensand). 



