crystallized Bodies contained in Lava. 47 



It is very probable that an explanation would be derived from 

 them more explicit still. In 1538 an eruption equally sud- 

 den raised the Monte Nuovo near Naples. 



" All those who have seen volcanoes in activity," saysM. 

 Fleuriau de Bellevue, " relate that nothing can equal the vio- 

 lence and immensity of their firts, and nevertheless some 

 people reduce their powers to those of our common furnaces." 



A volcano in a state of eruption presents a spectacle so 

 grand and imposing, that it seizes upon the imagination of 

 the spectator, and throws him into astonishment. This is an 

 effect of the extent of its lires, of the noise that accompanies 

 them, and of the spectacle of the currents of burning lavas. 

 But when we look with the eye of a philosopher, we soon 

 judge, from its effects, that this grand furnace has not in each 

 of its points an intensity of heat so great as that produced 

 in our melting furnaces. It may be easily conceived why our 

 furnaces have this greater intensity of heat. It is produced 

 by the continual currents of air introduced into them, which, 

 by their extreme rapidity incessantly bring with them a new 

 blast, the presence of which gives a greater activity to the 

 fire. This does not happen to the furnaces of volcanoes 

 which cannot have a communication, necessary for this great 

 activity, with the atmospheric air. This is the reason why 

 we see reduced to the state of glass, in a crucible in our 

 melting furnaces, the pyroxene schorl, which is unalterable 

 in the fires of volcanoes ; and we also obtain a complete vi- 

 trification of the fragments of lava which we subject to the 

 same experiments. 



Obsidian, or the compact glass of volcanoes, is that part 

 of their materials which has undergone the greatest degree 

 of heat. The vitrification of obsidian is complete ; none of 

 the pieces I ever saw exhibit any thing except glass, all the 

 substances composing it having l)een reduced to a perfect 

 fusion. These vitreous pieces proceed, therefore, from a 

 very strong heat produced in the volcano by some parti- 

 cular circumstance. 



Why do not these melted obsidians, which must cool as 

 slowly as the other lavas, present in their iutcnorany crystal- 

 lized 



