NOME VI. OBSIDIAN. 



463 



ful glass was discovered at Lipari by Spallan- 

 zani. 



" Black volcanic glass, rather porous, enamelled 

 with reticular lines of white felspar, which every 

 where penetrate it, and cross each other in differ- 

 ent directions : the black part is melted, the fel- 

 spar is only a frit. 



" On the summit of Mont Meisner, in Hessia, 

 are found isolated blocks, of a large bulk, of this 

 stony substance, whose base is incontestably vitri- 

 fied ; while the felspar has undergone but a slight 

 alteration. There is nothing extraordinary in this 

 fact, since the obsidians of Lipari not only afford 

 us a similar example, but also show us the felspar 

 in its state of crystallisation. 



" It is nevertheless proper to observe, that the 

 crystallised felspar, in the obsidian of Lipari and 

 other places, is an indication that this obsidian 

 owes its origin to a porphyritic rock, whose base 

 should be a trap, or a paste of felspar in mass ; 

 while the reticular felspar of the volcanic glass of 

 Mont Meisner seems to differ in its origin, and to 

 have had a base different from porphyries. 



" The disposition of this felspar, interwoven in 

 a vitreous black substance, recalled to my recol- 

 lection some stones which are not volcanic, of a 

 similar texture, which I possess in my collection 

 of rocks. I carefully examined them, and I per- 



I 



