( ^^2 ) 



■The Abbe Fortis affirms tbat he had 

 difcovered, In the pitch-ftone lavas of 

 Monte Brecaion, the evident tranfition of 

 petrofilex into pitch-iftone lava ; and on 

 comparing the analyfes of petrofilex made 

 by others, with thofe I have made of three 

 pitch-ftones, it will be found that they 

 perfeftly agree — with no other difference 

 deferving notice, but that the petrofilex 

 ufually contains no iron, of which a very 

 fmall quantity was found in the pitch-ftones 

 I analyfed. ' 



• As' it has been already fhowm, that 

 pltch-ftones that are not volcanic and 

 thofe which are, are of the fame genus, 

 I find little drfEculty in believing that 

 many of the latter are derived from the 

 former. 



In. all my refearehes relative to the rocks 

 of the volcanos in the two Sicilies, I have 

 always been attentive to difcover at what 

 degree of heat they fufe in our common 

 fire, that I might infer the adivity of the 

 ' ' fubterranean' 



