The Mineral Kingdom conſiſts of the foſſil ſubſtances found in the earth. Theſe are either entirely deſtitute of organic structure, or, having once poſſeſſed it, poſſeſs it no longer: ſuch are the petrefactions.

It is requiſite, for the proper diſcrimination of foſſils, to eſtabliſh certain characters, whereby they may, at all times, and in all places, be diſtinguiſhed from one another. The ſcience that teaches theſe is called Mineralogy.

As in the vegetable kingdom different methods have been formed upon the roots, the leaves, the flowers, the fruit, &c. ſo alſo in Mineralogy many methods may be deviſed, and there is no doubt of the utility of contemplating inorganic bodies in every point of view; for the more compariſons are multiplied, the more evidently do reſemblances or differences appear.

But as the chief object of the ſcience is to render foſſils ſubſervient to the uſes of man, it is evident that that method muſt be the beſt which diſplays their component parts: for theſe being well underſtood, we know what to expect from them; we accommodate our deſigns to their nature, and ſpend not our labour and money in vain attempts inconſiſtent with their inherent qualities.

There is a power implanted by the creator in organized bodies, which, upon the acquiſition of proper nutriment, unfolds and evolves the ſtructure which before lay concealed in the fecundated egg or ſeed. Similar veſſels, in each ſpecies, abſorb, convey, and aſſimilate the nouriſhment in the ſame manner; ſo that the appearance and ſtructure remain the ſame, unleſs peculiar cauſes prevent the accuſtomed courſe of things, and produce monſters: but this very rarely happens. Hence it is that the leading features or the external parts agree with the internal properties, and when judiciouſly choſen, form ſufficient characteriſtic diſtinctions.

But the formation of foſſils is totally different. Here no ſyſtem of veſſels collects, diſtributes, ſecretes or changes the concurrent particles, but they run together by chance, and are ſolely connected by the power of attraction; they are generally, too, of different kinds, rare and denſe, figured and ſhapeleſs, admitting of every poſſible variety. This general view of the ſubject ſhews us how little external characters can be depended on; but we ſhall more particularly conſider the principal of theſe.

Colour varies exceedingly, as does alſo the ſize of bodies. We cannot ſufficiently wonder at the violence done to nature by the ſtudied ſeparation of earths from ſtones. The conſequence is, that a ſtone of a certain ſize muſt conſtitute one genus, whilſt the ſame thing, reduced to powder, muſt be placed under another genus, which ſhall not be found even in the ſame claſs.

Hardness not unfrequently varies even in the ſame ſpecimen. Soft clay dries in the fire, and at length acquires the hardneſs of flint. Steatites (ſoap-rock) which may be ſcraped with the nail, and many other matters harden in the ſame manner, and that ſometimes without any notable loſs of weight; ſo that bodies paſs through every different degree of hardneſs, without any other change of their mixture.

Superficial characters are therefore inſufficient. They cannot even enable us to diſtinguiſh calcareous from other earths, for the efferveſcence with acids is a chemical mark, and happens, too, in matters of very different natures. To paſs over other inſtances, let him who is able diſtinguiſh the plumbum aeratum and plumbum phoſphoratum (§ 182. § 183.) by external appearances only!

Claſſes, Genera and Species are therefore to be formed upon the internal nature and compoſition; the varieties upon the external appearances. In ſuch a ſyſtem both methods conveniently agree.

Cronstedt firſt attempted this method, and with great ſucceſs; but afterwards the liquid analyſis, in which the illuſtrious Margraaf took the lead, better opened the internal ſecrets of nature; ſo that the excellent work of Cronſtedt now appears to contain many errors; theſe however are not to be attributed to any fault in the author, but to the inſufficiency of his experiments. The attempts of Mr. Pott by fuſion have long been known; but theſe however uſeful in other reſpects, rather tend to confound than to lay open the component parts of bodies.

In methodizing foſſils, compounds ſhould rank under the moſt abundant ingredient. Thus let a and b repreſent the component parts; if the former be the heavier, the compound muſt be placed under the genus of that: but this rule admits of ſeveral exceptions.

Thus, the properties of all ingredients are not of the same intenſity, if I may be allowed the expreſſion; ſome are more powerful or efficacious, ſo as to impreſs the maſs with their own genus and character, though forming leſs than half the weight. In ſuch a caſe the qualities are rather to be conſidered than the quantity, eſpecially if b ſo far from preponderating hardly ever amounts to half the weight.

Argillaceous earth (earth of allum) and magneſia are never found ſeparate, but almoſt always mixed with other things ſo that their weight conſtitutes the ſmaller part of the maſs: therefore if the above rule (§ 14.) was rigourouſly adhered to, theſe primitive earths would not be found amongſt the Genera, which would doubtleſs be an abſurdity.

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.