32 



OUR COMMON BRITISH FOSSIIS. 



ground on the other side until they are thin and 

 transparent enough to be properly mounted for 

 microscopic examination. In this way some exquisite 

 geological slides may be prepared. 



Fig. 'zi.—Spiro- 

 lociilina. 



Fig. 20. — Rotalina Voltziana. 



Common Foraminifera in White Chalk. 



Some of the limestones yield even still 

 more beautiful Radiolarians, although there 

 is little doubt that, in some way, the bands 

 of chert which run through our Carbon- 

 iferous and other limestones, have been species of 



Den talma. 



formed partly through the agency of these 

 siliceous-shelled animalcules, for we usually find them 

 absent where chert-bands occur, and present where 



