[Footnote 28: In the first part of this work, the distinction has been made of true volcanic productions, and those which are so frequently confounded with them; these last, though the creatures of subterranean fire, and bodies which have been made to flow in a fluid state, are clearly different from those masses of lava which have issued from a volcano, as has been there described. I would only here observe, that, according to this Theory, these bodies, which the Chevalier de Dolomieu here represented as lava and volcanic production, must be considered as unerupted lavas, which had been made to flow among the strata of the earth, where other at the bottom of the sea, or during those operations by which this land was erected above the level of the ocean.] On the one hand, the Memoir now before us represents this great effect as belonging to an unknown cause, so far as we are ignorant of that grand _débacle_ or _catastrophe_ which changed the situation of the sea. On the other hand, the Theory now proposed explains this operation, of forming those conical mountains of Sicily, and hollowing out its valleys, by known causes, and by employing powers the most necessary, the most constant, and the most general, that act upon the surface of the earth. But, besides explaining this change of land and water by an unknown cause, our author has here employed, for the removing of this mass of solid rock, powers which appear to me no ways adequate to the end proposed. The running of water upon the soft mud left by a river, given here as an example, corresponds indeed in some respects with the form of valleys; for, water acts upon the same principle, whether it makes a channel through the subtile sediment of a river, or through the travelled materials of a valley. But it is not here that there is any difficulty in conceiving the rivers of Sicily to have shaped the mountains and the valleys; it is in removing the masses of solid rock, which covered the whole surface of this land in successive strata, that any doubt could occur in ascribing the actual appearances of things to the natural operations of the earth; but it is here particularly that the retreat of the sea, in whatever manner supposed to be done, is altogether incompetent for the purpose which is now considered. I flatter myself, that when the Chevalier de Dolomieu, who has employed his uncommon talents in examining and elucidating the effects of fire in the bowels of those burning mountains, shall consider and examine the effects of time upon the surface of the earth, he will be ready to adopt my opinion, that there is no occasion to have recourse to any unknown cause, in explaining appearances which are every where to be found, although not always attended with such remarkable circumstances as those with which his labours have enriched natural history.