The value of a thing muſt likewiſe be conſidered. Minerals containing gold or ſilver muſt be ranked with thoſe noble metals although they hold three, four, or more times the quantity of heterogeneous matter. Not to mention other examples, pyrites are placed under the genus copper although they contain a much greater quantity of iron. This cuſtom, eſtabliſhed with the univerſal conſent of mineralogiſts, wants indeed a natural foundation, but it ſeems uſeful to miners to retain it; and the more ſo as it is certain that otherwiſe many minerals would be to be sought for under ſtrange and improper titles.
Laſtly, it muſt be remarked, that the ſolid ingredient determines the genus although the menſtruum be greater in quantity. Thus in magneſia vitriolata (Epſom ſalt) the earth gives the Generic name, although the vitriolic acid be the more ponderous. The same holds good in gypſum, allum, &c.
CLASSES
OF
FOSSILS.
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]].