288 ON A NATURAL SYSTEM 



CLXVIII. Species of organic FoJJils mineral!/- 

 ed by Salts. 



OHOANIC foffils, penetrated with fulinc mat- 

 ter, are but fcKlom found. Gypfum, indeed, 

 fometimcs contains the lefs perilhable remains 

 of animals and vegetables ; but thefe fubftances 

 are fcarce ever found quite gypfeous. Entire 

 animals are occafionaly to be met, filled with vi- 

 triol, (* 99.) and Rill oftener the harder parts of 

 vegetables, or their roots, fecni to rciill putrifac- 

 tioii by the means of ilii* fult. 



$ CLXIX. Earths. 



THE fecond genus, comprehending earthy 

 foflils, is by far the riche h Innumerable cal- 

 careous nuclei of fliell full and marine infecls 

 daily occur in calcareous llrata. Sometimes, an 

 animal covering, or ihcll, which \vasbefore cal- 

 careous, being changed in its internal texture 

 only, become fpataccous. 



Argillaceous nuclei of marine animals are com- 

 mon in aluminous fc hill us, but very rare in any 

 other bed. Frequently the covering of the a- 

 iiimalcule (lill remains. 



Marine exuvhu are obvious in marie alfo. If 

 lime predominates, often the Skeletons alone of 

 the fifh are feen. Of Olleocollu we have alrea- 

 dy fpoken fuflkiently, J 105. 



Siliceous 



