DOMAIN XII. VOLCANIC. 



dergo no change in this heat, not even 

 schorls or felspars ; and hence, though im- 

 mersed in the fiery torrent, they cannot 

 with propriety be called lavas ; as they are 

 not even softened by the mixture of bitu- 

 men, as stones of the argillaceous genus 

 are. 



" Between siliceous and argillaceous 

 stones there are many gradations, and va- 

 rious mixtures, which must occasion cor- 

 responding varieties in the effects which 

 heat, and various other circumstances, may 

 produce. It is sufficient here to establish 

 the principles on which most of them may 

 be explained. Compact lavas abound in 

 heterogenous substances, which have either 

 not been fused, or only partially fused, or 

 scorched, or decomposed by heat, as fel- 

 spar, schorls, garnets, zeolites, &c. Every 

 volcano has some that are peculiar to it. 

 Thus the lavas of Vesuvius abound in that 

 called white garnet, and which I call Ve~ 

 suvian; those of Etna abound in felspar, 

 &c. 



" Hence we must exclude from the rank 



