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which has been too rapid to change them into 

 lithoid lava. I consider even the perlstein of 

 Mr. Esmarck as an unverified obsidian : for 

 among the minerals in the kings cabinet at 

 Berlin there are volcanic glasses from Lipari, in 

 which we see striated crystallites, of a pearl gray- 

 color, and of an earthy appearance, form gradual 

 approaches to a granular lithoid lava, like the 

 perlstein of Cinapecuaro, in Mexico. The ob- 

 long bubbles observed in the obsidians of each 

 of the continents are incontestible proofs of their 

 ancient state of igneous fluidity ; and Dr. Thom- 

 son possesses specimens from Lipari, which are 

 very instructive in this point of view, because 

 fragments of red porphyry, or porphyry lavas, 

 which do not entirely fill up the cavities of the 

 obsidian, are found enveloped in them. We 

 might say, that these fragments had not time to 

 enter into complete solution in the liquified mass; 

 they contain vitreous feldspar, and augit, and are 

 the same as the celebrated columnar porphyries 

 of the island of Panaria which, without having 

 made part of a current of lavas, seem raised up 

 in the form of hillocks, like so many porphyries 

 in Auvergne, in the Euganean mountains, and 

 in the Cordilleras of the Andes. 



The objections against the volcanic origin of 

 obsidians, drawn from their speedy loss of color, 

 and their swelling by a slow fire, are deprived 

 of their force by the ingenious experiments of Sir 



