pierres naturelles des especes analogues, qu’elles ne peuvent en etre distinguees; voila egalement pourquoi les verres volcaniques eux-meme renferment encore des substances elastiques qui les font boursoufler lorsque nous les fondons de nouveau, et pourquoi ces verres blanchissent aussi, pour lors, par la dissipation, d’une substance grasse qui a resiste a la chaleur des volcans, et que volatilise la chaleur par laquelle nous obtenons leur second fusion.”

No doubt, the long application of heat may produce changes in bodies very different from those which are occasioned by the sudden application of a more intense heat; but still there must be sufficient intensity in that power, so as to cause fluidity, without which no chemical change can be produced in bodies.  The essential difference, however, between the natural heat of the mineral regions, and that which we excite upon the surface of the earth, consists in this; that nature applies heat under circumstances which we are not able to imitate, that is, under such compression as shall prevent the decomposition of the constituent substances, by the separation of the more volatile from the more fixed parts.  This is a circumstance which, so far as I know, no chemist or naturalist has hitherto considered; and it is that by which the operations of the mineral regions must certainly be explained.  Without attending to this great principle in the mineralizing operations of subterraneous fire, it is impossible to conceive the fusion and concretion of those various bodies, which we examine when brought up to the surface of the earth.]

The only question, therefore, which it concerns us to decide at present, is, Whether those operations of extreme heat, and violent mechanic force, be only in the system as a matter of accident; or if, on the contrary, they are operations natural to the globe, and necessary in the production of such land as this which we inhabit?  The answer to this is plain:  These operations of the globe remain at present with undiminished activity, or in the fullness of their power.

A stream of melted lava flows from the sides of Mount Aetna.  Here is a column of weighty matter raised from a great depth below, to an immense height above, the level of the sea, and rocks of an enormous size are projected from its orifice some miles into the air.  Every one acknowledges that here is the liquefying power and expansive force of subterranean fire, or violent heat.  But, that Sicily itself had been raised from the bottom of the ocean, and that the marble called Sicilian Jasper, had its solidity upon the same principle with the lava, would stumble many a naturalist to acknowledge.  Nevertheless, I have in my possession a table of this marble, from which it is demonstrable, that this calcareous stone had flowed, and been in such a state of fusion and fluidity as lava.