270 Observations ofi Volcanoes and their Lava. 



mountain : he calls them strad natiirali, sassi naturalii 

 thouajh ex'ery thing there he the work of fire. 



If M. HLimboldt had been a witness to the birth and 

 formation of the craters of which he speaks, he would soon 

 have given them up entirely to the volcanic empire. The 

 violence of the fire; the explosions and burning lava with 

 which that empire would have reclaimed them, would soon 

 have silenced all Neptunian pretension, and confirmed that 

 these masses, which he calls poyphyrr/, and their bases, 

 holding a medium betsveen obsidian and pitch-stone, are 

 lava and vitrifications belonging to Vulcan. M. Humboldt 

 derives his objection against the opinion that obsidian is 

 volcanic gla<;3, from its swelling up and becoming spongy 

 and fibrous by the least degree of heat of a furnace, whence 

 he concludes that it cannot be the production of fire. 



An attentive examination of volcanic productions shows 

 that their state and appearance depend on the nature of the 

 matters which have been subjected to the action of the 

 fires, on the degree of heat, the time and place where it has 

 been exercised. Therefore a degree of heat which has been 

 able to reduce any substance to compact glass, would not 

 be sufficient to put it into a state of ebullition, and at that 

 moment could not be carried to a degree capable of pro- 

 ducing that effect : to ihis the want of free air may contri- 

 bute. But there are some circumstances, even pretty fre- 

 quent, of volcanic fires giving fibrous and puffed-up glass. 

 I possess a vitrification from Lipari, the centre of which is 

 compact a,lass, and the inside in laminae, bubbles, and 

 threads, like pumice-stone. I have in my possession an- 

 other, part of which is glass nearly compact, and part glass 

 very much puffed up. I found on the sea-shore, 

 near Messina, two pieces of four or five inches in diameter, 

 formed merely of vitreous laminae, elongated, undulated, 

 and full of puffed up places. 1 have two fragments of 

 obsidian, or black compact glass of Ischia, one of the en- 

 tire faces of which evidently shows by the circular undula- 

 tions of the one, and the rounded inequalities of the other, 

 that they have been in a state of fusion. I saw at Vulcano 

 a vitreous mass, from which I broke a large fragment, the 

 glass of which is compact in some parts, and full of puffed 

 up places, some of them large and others small. Of this 

 kind is the black compact glass of the volcanoes of Iceland. 



Another objection of M. Humboldt is, that obsidian is 

 found in such large masses that it may be compared to a 

 quarry. But why should this be an objection ? Vitreous 

 lava, does not differ from any other lava, but by more perfect 



" " ' vitrification J 



