Outlines of mineralogy

Foſſils externally reſembling animals or vegetables, originate from foreign matters, which by ſome peculiar proceſs are changed in the boſom of the earth, or are ſo impregnated by mineral particles gradually occupying the place of thoſe which have putrified, that they no longer reſemble organic ſubſtances, except in figure.—Theſe are commonly called Petrefactions.

The harder ſhells of animals expoſed to the weather, are not always exempt from deſtruction; for their gelatinous matter being gradually deſtroyed by putrefaction, they become brittle, and in a manner calcined. In leſs expoſed ſituations, ſome of them preſerve the nature of their materials, but acquire a ſpar-like texture.

We muſt carefully diſtinguiſh betwixt the foreign bodies themſelves, changed or petrified, and their impreſſions upon the ſurrounding matrices. Sometimes the body is entirely deſtroyed, forming a cavity in the ſurrounding matter, and this cavity afterwards is filled with other materials. Nuclei, or kernels, are likewiſe found, formed within the cavities of the harder ſhells, and bearing the form of their internal ſurface.

I am far from thinking the knowledge of petrefactions is barren and uſeleſs. We may, and ought, to conſider them as medals depoſited by the hand of nature, in memory of the more remarkable changes on the ſurface of the earth, and from which the time and order of the work may, in ſome meaſure, be judged of, whilſt other monuments are ſilent. Theſe, being properly interpreted, ſhew us their native ſituations in the former ſtate of the ſurface of the earth, and teach us the unbounded empire of the ſea, and the conſequent changes. By them we learn to diſtinguiſh the ancient and modern foundations of the mineral kingdom; for thoſe which are not formed of petrefactions, and never contain them, are doubtleſs of greater antiquity than animals or vegetables; and, laſtly, by their figure they ſhew us the inhabitants of our globe, eſpecially thoſe of the greateſt depths of the ocean.

Mr. Cronstedt has admirably arranged the petrefactions; we think it right, therefore, to retain his method. The Genera are built upon the Genera of foſſils, and arranged like the four claſſes thereof; the ſpecies upon their ſpecies, and the varieties upon the organic ſubſtances that have been changed. The following are the Genera hitherto diſcovered.

Saline Calcareous Earth with an organic Form.

Gypſeous petrefactions are very rare.

Saline Iron with an organic Form.

Human bodies have ſometimes been found indurated and penetrated by vitriol of iron; so likewiſe have plants, their roots eſpecially. In the open air they moulder away.

Mild Calcareous Earth with an organic Form.

This conſtitutes the ſubſtance of moſt petrefactions.

It is remarkable, that petrefactions found in clay are compreſſed, although, in ſubjacent calcareous ſtrata, they preſerve their natural figure. Similar compreſſed petrefactions are alſo found in the marly ſchiſtus.

Siliceous Earth with an organic Form.

Siliceous petrefactions are ſometimes met with, but, in general, this material forms only nuclei (§ 264). Trunks of trees are ſometimes found changed into agate. The celebrated Ferber has ſeen petrefactions in chert and jaſper, and the illuſtrious Born mentions corallines (porpitæ) in ſinople or martial jaſper.

Earth organic.

Animals and vegetables are reſolved by putrefaction into an earth, which may be regarded as forming a peculiar genus, until every appearance of organization being obliterated, at length it comes to be conſidered as common earth.

Wood, penetrated by indurated petroleum, forms a remarkable variety of coal.

Silver with an organic Form.

Native ſilver is ſometimes inherent in petrefactions, but never, to my knowledge, conſtitutes the ſubſtance of them, unleſs mineralized with copper and ſulphur.

Quickſilver in an organic Form.

When mineralized by ſulphur, it ſometimes, though very rarely, conſtitutes petrefactions.

Copper with an organic Form.

Bones and teeth are ſometimes found replete with the blue calx of copper. Bits of copper pyrites often ſtick in petrefactions, but ſeldom conſtitute their whole ſubſtance. I have some such from Norway, in a matrix of magnetical iron ore.

Calciform iron ſometimes is found in the ſhape of roots and branches of trees. When mineralized by ſulphur, it frequently exiſts in petrefactions, but ſeldom conſtitutes the whole maſs.

Zinc with an organic Form.

I have ſeen pſeudo-galena (black jack), in the form of coral.

Some modern writers, as well as Mr. Cronstedt, place the productions of volcanoes in an appendix by themſelves; but, I think, to no good purpoſe. Things formed by the hand of nature, whether by a liquid or a dry proceſs, muſt not be diſjoined; for ſhe frequently avails herſelf of both methods in one and the ſame inſtance. And, indeed, the origin of many things is ſo very doubtful, every veſtige thereof being obliterated, that even an Œdipus could not with certainty determine how they were produced. And, on the other hand, many aſſert, that almoſt the whole of the mineral kingdom is the product of fire. To avoid error, therefore, it is better to claſs foſſil ſubſtances according to their conſtituent parts, which proper experiments will lay open to us; for we can seldom know their origin or formation.

Homogeneous ſubſtances joined together, but not primitive, will find a place among the ſtones, or elſewhere, in the firſt appendix.