302 DOMAIN XII. VOLCANIC. 



of that of Faujas, being extremely simple 

 5 and confined ; and he confirms the idea 

 which I have long since advanced, that all 

 lavas consist of siderite and felsite. The 

 former, with Saussure and other writers, he 

 calls pietre cornee, being a corneus of Wal- 

 lerius*. 



The study of extinct volcanoes he con- 

 siders as, perhaps, more interesting to the 

 naturalist, than that of the activef. Not 

 only has Vesuvius been repeatedly quite 

 extinct for centuries; but even the tre- 

 mendous and eternal Etna was quiescent 

 from 1447 till 1537- The basaltic prisms, 

 as already mentioned, he regards as the 

 undoubted products of submarine volca- 

 noes ; and his account of their origin may 

 more accurately be expressed in his own 

 words. 



origin of " As a perfect dissolution is necessary in 

 order to form perfect crystals, so a perfect 



* P. 291, 343, 173. 



f " Lo studio dei volcani ardenti non essere il solo che possa per- 

 fezionare la scienza; che quello degli estinti e, a certi riguardi, piu 

 fecondo di lumi, e non meno del primo degno dell' attenzione, e 

 della premura del NaturalUta." Disc. Prel. p. iv. 



