194 Mr. BowERBANK on the Siliceous Bodies of the Chalk, S^c. 



maimer, the whole of the cartilaginous parts being frequently replaced by pyrites ; 

 and in other cases, as the fossilized crabs, where the animal matter contained 

 within the shell has exuded slowly from the body, we trace its influence upon the 

 surrounding matrix which had been impregnated with it ; for in all the masses of 

 indurated clay containing such remains, the hardness increases in proportion as we 

 approximate to the body of the animal. The same law is also very happily illus- 

 trated by the state in which we usually find the remains of Belemnites in the lias 

 shale of the Yorkshire coast ; the anterior portion of the Belemnite being gene- 

 rally free from pyritical remains, while the alveolus is enveloped by a mass of in- 

 durated clay, which is universally found to become harder and more pyritical as 

 we cut down towards the body of the animal. 



Numerous other cases might be cited to illustrate the importance of the presence 

 of the animal matter in the formation of the fossil, and to prove that it is to this 

 agent more than to the presence of the mineral substances in the original body, that 

 we are indebted for the preservation of these interesting remains of the former 

 inhabitants of the earth. 



