( '3S ) 



preferved, and in the fame ftate in which 

 it was thrown out of the fire, of which 

 the lava now defcribed is an evident ex- 

 ample. 



At the diftance of another full mile from 

 the place whence I took my departure, the 

 mountainous coaft of the ifland becomes 

 fomewhat more level ; and on this plain 

 arife detached mafles of porphyry, which 

 fhew no figns of having been touched, 

 much lefs fufed, by the fire. It is of a pe- 

 trofiliceous bafe, of the colour of brick, af- 

 fords fparks with fteel, and is extremely 

 compadl, and without pores, except a few 

 fuperhciai vacuities, coated with a thin 

 white cruft of carbonate of lime, fometimes 

 iludded with cryftals of the fame kind. 

 Thefe fmall geodes, which have been pro- 

 duced, without doubt, by filtration, are 

 decompofed in a fe\Y moments by the nitric 

 acid, and dilToIve with a ftrong effervef- 

 cence. This porphyry, in its hardnefs, po- 

 lifh and luftre, is not inferior to the Egyp- 

 tian. Befides flioerls, it contains numerous 



cubical 



