( 28o ) 



we may remain in doubt whether the vol- 

 canized rocks that prefent themfelves to 

 our view, have ever actually flowed. This 

 doubt I experienced myfelf, when I firft 

 vifited the Euganean mountains, in confe- 

 quence of u-.y obfervations relative to the 

 primitive rocks, and the experiments I had 

 made on lavas in the furnace. I conGdered 

 that it was poflible the rocks of the Fuga- 

 nean hills m'ght never have flowed in cur- 

 rents, and confequently that they could not 

 have been lavas, though they might bear 

 very fenfible trarks of fire, and even the 

 fame with vitreous lavas ; as I was con- 

 vinced from the experiments I had made 

 in the furnace, which, without wandering 

 too far from my fubje(3:, I will here briefly 

 defcribe. 



In Chap. XI, I have fpoken of the fufion 

 of fome porphyries with a horn-flone and ■ 

 petrofiliceous bafe. The following are the 

 appearances I obferved fome time before 

 their fufion. The pieces, though before 

 their fractures were fcabrous and angular, 



afljjmed 



