227 



mountains far from any active volcano. It is 

 thus that we find obsidians between Llactacunga 

 and Hambato, in the kingdom of Quito, cover- 

 ing the space of a league square ; and in Hun- 

 gary, where they were accurately examined by 

 Mr. Esmarck. This singular position made the 

 Danish mineralogist think, that they belonged to 

 the secondary or floetz formation ; and that the 

 volcanic fire had traversed the strata of pumice, 

 as well as the obsidians and the basalts, which 

 he equally considers as not of volcanic origin. 

 A third variety of pumice is that with fragile 

 fibres, somewhat thick, transparent on the edges, 

 and of an almost vitreous lustre, which exhibits 

 the transition from the granitic pumice stone to 

 the capillary glass. This variety, which is ad- 

 herent to the green and grayish obsidian of the 

 Peak of Teneriffe, seems to have been produced 

 by the action of the fire on matters already vi- 

 trified. 



From the whole of these considerations it re- 

 sults, that it is as erroneous to consider the whole 

 of the pumice stones as tumefied obsidians, as 

 to look for their origin exclusively in granites 

 rendered fusile and fibrous by the action of fire, 

 or of acid vapors. It is possible, that the ob- 

 sidians themselves were only liquified granites 



* We meet sometimes, though very rarely, with mica in 

 the obsidians : and Dolomieu thinks he has found not only 

 feldspar and mica, but also quartz, in the granitic pumice. 



Q 2 



