Notice of Active and Extinct Volcanos. 24.9 



traded by the usual modes, with the addition of five per cent, 

 of sub carbonat of potass, to make it crystalize, there not 

 being sufficient alkali in the stone. 



Opal and hyalite are found in the trachyte of Hungary. 



The geological portion of the different varieties of trachyte, 

 is stated to be constant. 



1. Trachyte, properly so called, in the centre of the group. 



2. Trachytic conglomerate surrounding the flanks of the 

 mountain. 



3. Trachyte-porphyry — the pearl stones and the millstone 

 porphyry intermediate. 



" The following is a synopis of the genus Trachyte, as given 



by Beudant. 



1st Species, Trachyte, properly so called. 



1st variety granitoid, no apparent cement, numerous crystals of 

 glassy felspar, confusedly united ; crystals of black mica ; 

 hornblende rare. 



2nd, with mica and hornblende — these crystals abundant, and gene- 

 rally black ; paste of compact felspar, pretty pure, and fusible 

 into a white enamel ; crystals of glassy felspar. 



3d, porphyritic — paste of compact felspar, fusible into a white 

 enamel; crystals of felspar, glassy, lamellar, and compact ; au- 

 gite more or less abundant; no mica or hornblende. 



4th, black, — the paste black, dull, fusible into a white enamel, 

 with black spots, more or less numerous, disseminated ; crys- 

 tals of glassy felspar, sometimes of augite. 



5th, ferruginous, paste ferruginous, dull, of a red or brownish 

 color, blackening when heated; fusible into a black or scori- 

 form enamel ; crystals of glassy felspar; numerous crystals of 

 black mica. 



6th, earthy or domite, paste earthy, porous, light-colored ; crys- 

 tals of glassy felspar rare ; crystals of black mica abundant. 



7th, semi-vitreous, (Pseudo-basalte of Humbolt,) paste semi-vitre- 

 ous, black or brown ; fracture large-conchoidal, losing its color 

 in the fire, and melting into a white enamel. 



8th, cellular, paste of various descriptions ; contains numerous 

 cells more or less imperfect, either round or elongated. 

 2d Species, Trachytic Porphyry. 



1st Subspecies, with crystals of quartz ; base of compact felspar, 

 with or without lustre, more or less abundant, containing most 

 commonly a great number of small semi-vitreous globules ; 

 crystals of quartz, more or less numerous ; crystals of glassy 

 felspar, generally well denned ; black mica, in small hexago- 

 nal plates more or less numerous. 



Vol. XIII.— No. 2. 7 



