( S4 ) 



produdtioii of this great accumulatiGn cf 

 vitreous bodies by fubterranean fires. It is 

 certain that the produdion of pumices, 

 enamels, and glafl'es requires a greater heat 

 than the fimple fufion of lavas, when thefe 

 fubflances derive their origin from the fame 

 bafe ; but we (hall not find it neceflary that 

 this greater heat fhould be extremely vio- 

 lent, if we confider the kinds of flones 

 from which thefe vitrified mountains have 

 been produced. The greater part are felt- 

 fpars, and petrofilex, with fome fmall quan- 

 tities of horn-fione. As to the latter, it has 

 .already been fhewn that it eafily vitrifies in 

 a glafs furnace with no very vehement fire-; 

 In which, likewife, many petrofilices and 

 fome feltfpars are vitrifiable *. It has alfo 

 been feen that the glafles, pumices, and 

 enamels of Lipari are all completely re- 

 fufed in the furnace. It appears to me, 

 likewife, that w^e have pofitive proofs that 

 the volcanic fire was lefs violent than that 

 of the furnace, in the fubftances, as well 



■ * See Chap. V. and Chap. XI. 



crvftallized 



