Part 31

§ 267.

Gypſeous petrefactions are very rare.

Saline Iron with an organic Form.

§ 268.

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.

§ 269.

This conſtitutes the ſubſtance of moſt petrefactions.

Clay with an organic Form.

§ 270.

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.

§ 271.

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.

§ 272.

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.

Petroleum impregnating organic Bodies.

§ 273.

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

Silver with an organic Form.

§ 274.

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.

§ 275.

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

Copper with an organic Form.

§ 276.