DOMAIN XII. VOLCANIC. 



HYPONOME II. PORPHYRITIC. 



This kind, spotted with decayed crystals of fel- 

 spar, may be found in most of the preceding sites. 



Faujas gives the following examples. 



" Obsidian, with crystals of white felspar, which 

 have preserved their form and colour, and which 

 are rather frits than melted. 



" Obsidian of a very sharp fracture, with a 

 number of little round and oblong globules of a 

 dull white substance, which resembles amel, and 

 which may proceed from a granular felspar, spread 

 in great abundance in the paste of the stony sub- 

 stance which has given birth to that beautiful 

 black glass, spotted with white. The paste of this 

 obsidian should be fusible; for the glass which 

 results from it is pure, and although it appears 

 of a deep black in contrast with the white spots, 

 it is of a fine transparency on the edges, and rather 

 white than black, but of a smoky white : found at 

 Lipari. Some specimens of this volcanic glass 

 are seen in which the same white substance, in- 

 stead of being disseminated in the mass, is dis- 

 posed in small layers, very thin, of the thickness 

 of half a line or a line at most, which alternate 

 with layers of glass, very black and shining, of 

 four, five, or six lines in thickness. This beauti- 



