Fossils are of four kinds, viz. ſaline, earthy, inflammable, and metallic; hence ariſe four claſſes.
Salts, or ſaline ſubſtances are more or leſs ſapid, and when finely powdered diſſolve in at leaſt 1000 times their weight of boiling water. They melt in the fire, which for the moſt part changes or deſtroys them[5].
Earths are inſipid, not ſoluble in water in the degree mentioned above (§ 20) though perhaps water in Papin’s digeſtor will diſſolve ſome if not all of them, eſpecially if their ſurface be greatly increaſed by a previous ſolution in and precipitation from ſome other menſtruum. In the chain of nature they are by inſenſible gradation joined to the ſalts, ſo as not to be diſtinguiſhed without artificial limits. Their form is not changed by a moderate heat, nor are they diſſipated by a violent one. Their ſpecific gravity is to water, leſs than 5 to 1.
Inflammable foſſils abound with phlogiſton, do not unite with water, but when pure diſſolve in oils; expoſed to the fire, they ſmoke, generally inflame, are for the moſt part conſumed, and ſometimes totally vaniſh.
Metals when perfect do not diſſolve at all in water; only a few of them in oils, and then only when in part deprived of their phlogiſton. They are the heavieſt of all known ſubſtances, the lighteſt of them weighing more than ſix times its bulk of water.
They melt in the fire with a ſhining ſurface, and in clay veſſels the ſurface is convex.