NOME VI. OBSIDIAN. 449 



consider it as one of those volcanic bodies which 

 constitute the middle substance between enamels 

 and glasses. 



" In my description of the glasses of Lipari, Venuiar. 

 I have observed that several of them are inter- 

 sected with veins or earthy leaves, by means of 

 which they are easily divided into plates. The 

 same is observable in the present glass, in which 

 we find the same quality as in some marbles, 

 which being cut in the vein may be divided, 

 without any great labour, into large slabs, but 

 which break into small pieces if it be attempted 

 to divide them in any other manner. Some of 

 the workmen who dig the pumices, and were 

 very useful companions to me in my excursions 

 to Campo Bianco and the Monte della Castagna, 

 at my request drove, with heavy hammers, an 

 iron wedge into these earthy veins, and extract- 

 ed from the common mass of this glass, large 

 plates five feet long, three broad, and two in 

 thickness. To the surface of each plate was at- 

 tached a coating of hard earthy matter, which 

 still more confirmed me in the opinion I have 

 already given, that this matter had resisted fu- 

 sion, and, being lighter than the fluid glass, had 

 ascended to the surface; a conjecture further 

 corroborated by the artificial fusion which I 

 made of this glass retaining some portion of this 



VOL. II. 2 G 



