( 3^2, ) 

 fubterranean conflagrations by which they 

 have been, inelted. I have proceeded in 

 the fame manner with refped to the volca- 

 nic rocks 6f the Euganean mountains, em- 

 ploying conftantly the fame fire, I mean 

 that of the glafs^furnace. As to the bafes 

 of thefe rocks, we have already feen that 

 not one of them proved refradory, not 

 even excepting the hardeft and moft corn- 

 pad petrofilices, which have formed cur- 

 rents. The feltfpars arid micas, with which 

 the Euganean lavas fo abound, appeared 

 equally fufible. 



The eafy fufibllity of the feltfpars excited 

 in me fome furprife, when I confidered the 

 infufibility which, if not conftantly, is very 

 frequently the property of the fame (lones in 

 the rocks of other volcanos when expofed to 

 the fame degree of heat -, and, as I obtained 

 the fame fufion when the Euganean feltfpars 

 v,^ere detached from their bafe, it cannot be 

 alleged that this bafe ferved as a flux. A dif- 

 ference f6 remarkable, it feems probable, can 

 only proceed from the different proportionfi 

 z of 



