( ir6 ) 



ever, extremely compa£l, and will readily 

 give fparks with ileel, and cut common ar- 

 tificial glafs. Several of thefe pieces con- 

 tain within them fmalt white particles, whicb 

 have been obferved and defcribed in many 

 of the glaiTes of Lipari, which particles in- 

 dicate that the glafs containing them is not 

 fo perfedlly vitrified as the reft. We alfo 

 find pieces, though they are rare, the one 

 half of which is a very black glafs, and the 

 other a fimple lava. The lava, which thus^ 

 forms a whole with the glafs, is of a cineri- 

 tions colour, and, as appears from fome 

 analyfes which I have made of it, is of a 

 petrsfilkeous bafe. 



Tills glafs, like other volcanic glafles,. 

 changes in the furnace into a vitreous froth. 



It now remains to fpeak of the pumices,, 

 which are likewife enveloped in thefe tufas.- 

 Thefe never form laree maOes, but are al- 

 ways found in detached pieces, of rather a- 

 imall iize, the largeft rarely exceeding the 

 bignefs of the clofed hand. In general they 



are 



