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often been found on the quartz that inveloped it*. This 

 laft muft therefore have been in a foft ftate, while the ihorl 

 was in a hard ftate ; now this could not happen if the quartz 

 were foftened by heat, for fliorl, being infinely more fufible, 

 muft have been in a foft ftate alfo, and concrete long after the 

 quartz : nay, if we credit Mr. Gerhard and others, cryflal 

 has been deteded in a foft flate. We have already quoted Mr. 

 Laffone as an eye witnefs of the aqueous formation of filiceous 

 ftones. I Ihall only add, that petrofiliceous and other fufible ftones 

 of this clafs have quite a different afpecfl when they pafs through 

 a ftate of fufion from that which they prefent in their natural 

 ftate. I alfo pafs over the mofTes and other vegetable and 

 animal fubftances inclofed in agates, &c. as our author pre- 

 tends to account for their prefervation in the midft of the 

 moft raging heat by virtue of a compreflion, originating, one 

 knows not how, which prevents their combuftion or charring. 



Let us now examine the principal proofs which oiar author 

 adduces in fupport of his fyftem ; that from the infolubility 

 of calcareous ftones we have already obviated. 



ift, " There are fpecimens of foffd wood which bear the 

 •' moft evident marks of having been injeded with a flinty 

 " fubftance in fufion. This appears from the wood being pene- 

 " trated partially, fome parts not having been penetrated at all. 



" In 



* 2 Rome 267 in Note, i Chy. Ann. 1786. p. 174. 



