NOME VI. OBSIDIAN. 467 



duced by subterranean fires, this difference only 

 relates to a greater opacity, and a more unctuous 

 and resinous aspect which amels possess ; while 

 the glasses, of whatever colour, have a brighter 

 lustre, are more crystalline, and seem better 

 melted. 



" Real pitchs tones, whatever may be their co- 

 lour and their vitreous appearance, must not be 

 confounded with glasses and amels: they are 

 foreign to them. 



" 1. Grey amel, with shades of a grey white, 

 rather greenish, with a fracture rather stony than 

 vitreous. Its contexture, and the vesicles seen in 

 its paste, leave no doubt of its being a volcanic 

 amel. In observing it with a lens, crystals of fel- 

 spar, which characterise its porphyritic origin, are 

 even perceived. This variety comes from Ascen- 

 sion Island, where it was collected by M. de 

 Berth, an able mineralogist, who has some fine 

 collections of lavas from the isles of Bourbon and 

 France. 



"2. A yellowish grey amel, rather reddish, 

 with a resinous fracture. If I may be allowed to 

 use the expression, it is what Dolomieu has called 

 resiniform lava. Its grain, its fracture, its semi- 

 vitreous paste, all indicate its being an amel ; and 

 the crystals of felspar, distinguished on polished 

 faces, announce that this amel owes its origin to 



2 H 2 



