STUDY IV. 271 



fliells are llkewife found in great quantities, fo that 

 as marl has been evidently formed of their wreck, 

 it appears to me extremely probable, that the flints 

 have been compofed of the very fubftance of the 

 fifhes which were there inclofed. 



This opinion will appear lefs extraordinary^ if 

 we obferve that many of the comes d'ammon, and of 

 fingle-flielled foffils, which, from their form, have 

 refifled thepreflure of the ground, and not being 

 compreflTedby it, have notejeded, like thedouble- 

 flielled, the animal matter which they contained, 

 but exhibit it within them, under the form of cryf- 

 tals, with which they are ufually filled, whereas 

 the two-(helled are totally deftitute of it. 



The animal fubftances of thefe laft, I prefume, 

 confounded with their cruQied fragments, have 

 formed the different coloured paftes of marble, 

 and have communicated to them the hardnefs and 

 polidi of which thefe marbles are fufceptible. This 

 fubftance prefents itfelf, even in fhell-fifh when 

 alive, with the charaders of agate, as may be feen 

 in feveral kinds of mother-of-pearl, and among 

 others, in the half tranfparent, and very hard knob, 

 which terminates what is called the harp. Finally, 

 this ftony fubftance is found, befides, in land ani- 

 mals ; for I have feen, in Silefia, the eggs of a fpe- 

 eies of the woodcock, which are highly prized in 



that 



