2 



found in their native state and situations. But as the term 

 fossil, alone, declares these bodies, bearing the obvious and 

 characteristic marks of vegetable or animal organization, to 

 have been obtained from the mineral kingdom, the employ- 

 ment of any of these epithets appears to be unnecessary. 



By whatever mode organic remains, in subterranean or 

 subaqueous situations, may be preserved from resolution 

 of their substance for a considerable time, it is obvious that 

 they must be liable to be impregnated with whatever 

 matters may be held in solution in the fluids with which 

 they may be thus imbued. From this source mineral 

 matters may be deposited, by intromission, into the original 

 interstices and cavities of the organic body ; or may, by 

 substitution, fill the spaces which have been produced by 

 the partial removal of the original organic substance ; or 

 lastly, may, by impregnation and consolidation of the che- 

 mically altered organic matter itself, produce the several 

 earthy or metallic fossils. 



The earthy substances which enter into the composition 

 of fossils, or, as in these cases they may be termed petri- 

 factions, are chiefly of the calcareous, siliceous, and argil- 

 laceous kinds, in different states, and in various mixtures. 

 The most common of the calcareous genus are the several 

 species and varieties of carbonates ; limestone, marble, 

 stinkstone, chalk, spar, oolite, &c. Fluate of lime some- 

 times occurs as the matrix, and, rarely, it forms the sub- 

 stance of fossils. Sulphate of lime, though sometimes found 

 crystallized in their cavities, has not been mentioned as 

 forming the substance of fossils. Sulphate of barytes, or 

 baroselenite, is said sometimes to form the substance of 

 fossils, but the instances are very rare. Silex enters, in 

 different combinations, into the composition of fossils : 

 quartz, chert, agate, calcedony, jasper, flint, pitchstone, and 

 semiopal, have all been found forming their substance or 

 constituting the masses in which they have been contained. 



