NOME VII. VOLCANIC JNTRITE. 



of obsidian to black volcanic glasses*, whatever 

 may be their opacity and their brilliancy, more or 

 less unctuous, or their paste more or less vitreous, 

 provided that their transparency is visible on their 

 edges in the thinnest fractures of these glasses. 

 The preceding number forms the transition of 

 black amel to the obsidian of the Ascension Island, 

 of Teneriffe, of Stromboli, Yulcanp, p." 



NOME VII. VOLCANIC INTRITE. 



This denomination, as in the other divisions, 

 includes those substances which, on a base, pre- 

 sent crystals of various natures ; and which have 

 thence often been vaguely styled porphyries. 

 Real porphyritic lava has already been consi- 

 dered, under the Nome Compact Lava ; being 

 one of the most common appearances of jthat 

 kind, and scarcely distinguishable from genuine 

 porphyry, with a base of basaltin and crystals of 

 felspar. 



The most remarkable and singular volcanic 

 intrite is that with leucite, a crystal resembling with leucite. 

 a white garnet, and at first so named, which 

 seems peculiar to the lavas of Vesuvius, and of 



* Obsidian may be of several colours, as already mentioned. 



