( 3o8 ) 



of to fo great a depth, but for the fiery 

 torrents that have iffued^ from it. 



Three different bafes of the Euganean 

 lavas have engaged my attention ; the 

 feltfpar in the mafs, the petrofilex, and 

 the pitch-fto-^e. The former of thefe is 

 changed by the adion of the fire into a 

 vitreous lava, the equal to which I have 

 not feen among the produds of any other 

 volcanos that I have examined. It has 

 been already obferved, that in the Eolian 

 ifles the feltfpar in the mafs has contributed 

 to the formation of many lavas ; but thefe 

 cannot claim the name of vitreous, as 

 they retain more or lefs of the external 

 appearance of the feltfpar ; or this felt- 

 fpar has paffed immediately into glafs or 

 enamel. 



The petrofilex, likew^ife, forms a kind 

 of general exception with refped to the 

 Eolian volcanos. We have feen that 

 m^ny of their lavas have the petrofilex 



for 



