NOME VI. OBSIDIAN. 465 



The remarkable isle of Pentellaria, between 

 Sicily and Africa (the ancient Cossura, of which 

 there are coins), produces a black obsidian of so 

 unctuous an aspect that Ferrara compares it to the 

 bitumen of Chaldea. It is perfectly opake, even 

 in the thin edges ; and has numerous crystals and 

 quadrilateral plates of felspar in perfect preserva- 

 tion, except that it has a dry aspect, and is stunned 

 in some parts. The pieces more free from felspar 

 are extremely hard, with a conchoidal and often a 

 striated fracture like common glass. When rub- 

 bed they yield a powerful smell of burnt hair*. 



HYPONOME VII. VOLCANIC AMELS. 



Faujas, in his classification of volcanic pro- Description bj 

 ducts, has so amply treated this curious subject, 

 that his account deserves to be translated, for the 

 benefit of the English readerf . 



" When compact lavas, either prismatic or 

 amorphous, are fused in a crucible in the furnace 



* Ferr. 258 ; odore di capelli Iruciati. Would this express the 

 undefinable smell of quartz ? v 



i -f Annales du Museum : but much altered and greatly enlarged in 

 the second volume of his Essai de Geologic, Paris, 180Q, 8vo. At 

 first there were seven, but now twelve, classes, injudiciously chosen, 

 md arranged from trifling objects and circumstances; while. some 

 important substances are omitted. But there are many novelties, 

 md ingenious observations, as usual, in the works of Faujas. 



The former edition is preferred, for the reason already a 

 VOL. IT. 2 H 



