450 DOMAIN XII. VOLCANIC. 



earth, which with difficulty fused, though the 

 glass was inflated, and changed into a frothy 

 enamel. 



" This glass slightly cuts the factitious glass ; 

 and if the cutting angle of one piece is driven 

 with force along the surface of another, it pro- 

 duces a white and impalpable powder. 



" 5t Tnis s P ecies of gl ass completely deserves 

 that appellation, since it is not only the most 

 perfect of all the volcanic glasses of the Eolian 

 isles, but does not in the least respect yield to 

 what is called the Iceland agate, or the pietra di 

 galinazzo of Peru, which is supposed to have 

 been the obsidian stone of the ancients. In the 

 large pieces its colour is extremely black, and it 

 is entirely opake, but the thin leaves are white 

 and transparent : the opacity and blackness may 

 be said to be in the direct ratio of the thickness. 

 This glass, which is extremely compact, is free 

 from aeriform bubbles, and from every kind of 

 heterogenousness. It is somewhat harder than 

 the fourth species, and therefore cuts factitious 

 glass more easily, and gives more sparks with 

 steel. Its edges are sharp and cutting. 



" M. Faujas, having obtained some specimens 

 of the best glass of Lipari, has made some ob- 

 servations on it proper to be given here. He 

 admits that this species is the same with that of 



