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pulverulent. The experienced, however.^ 

 may ftill difcern within it the vitreous 

 lineaments ; and I am convinced that, were 

 a deep excavation to be made in this lava, 

 we fhould more completely difcover its vi- 

 treous nature ; as, by the fame means, we 

 afcertain the real quality of other ftones, 

 both natural and volcanized, the furface of 

 which has been changed by the adion of 

 corrofive agents. 



In the internal part of this decompofed 

 lava, we find feveral globes of petrofilex as 

 ftrongly charadlerized as in the natural 

 ftate. As it is detached, I dare not num- 

 ber it among the lavas. Similar to many 

 congenerous ftones, it is furrounded v/ith 

 a white argillaceous cruft, which attaches 

 to the tongue ; and contains a number of 

 micaceous points, and feltfpathofe lamiuci?. 



In the furnace it becomes white, and 

 acquires: a thin vitreous coating : the 

 pieces^ however, do not lofe their primitive 

 figure. 



II. This 



