Every thing, therefore, tends to show that the surface of the earth must wear; but M. de Luc, although he allows the principles on which this reasoning is founded, labours to prove that those destructive causes will not operate in time. Now, What would be the consequence of such a system?--That the source of vegetation upon the surface of the earth would cease at last, and perfect sterility be necessarily the effect of allowing no farther degradation to the surface of the earth; for, What is to supply the matter of plants? Water, air, and light alone, will not suffice; there are necessarily required other elements which the earth alone affords. If, therefore, this world is to continue, as it has done, to form continents of calcareous strata at the bottom of the ocean, the animals which form these strata, with their _exuviae_, must be fed. But, on what can they be fed? not on water alone; the consequence of such a supposition would lead us to absurdity; nor can they be fed on any other element without the dissolution of land. According to my views of things, it is certain that those animals are ultimately fed on vegetable bodies; and it is equally certain, that plants require a soil on which they may not only fix their fibrous roots, but find their nourishment at least in part; for, that air, water, and the matter of light, also contribute, cannot be doubted. But if animals, which are to form the strata of the earth, are to be fed on plants, and these are to be nourished by the matter of this earth, the waste of vegetable matter upon the surface of the earth must be repaired; the exhausted soil must be transported from the surface of the land; and fertility must be restored by the gradual decay of solid parts, and by the successive removal of soil from stage to stage. What a reverie, therefore, is that idea, of bringing the earth to perfection by fixing the state of its vegetable surface! The description of those natural operations, which M. de Luc has given with a view to establish the duration of the mountains, is founded upon nothing but their destruction. These beds of rivers, which, according to our author, are _hardly_ to be wasted any more, will not satisfy a philosopher, who requires to see no degree of wasting in a body which is to remain for ever, or continue without change. But, however untenable this supposition of a fixed state in the surface of this earth, the accuracy of the natural philosopher may still be observed in the absurdity of the proposition. «L'état des _montagnes_ sera _fixe_, partout où les _rivières_ seront arrivées au point de n'emporter pas plus de limon hors de leur enceinte, que l'air et les pluies n'y déposeront de _terre végétable_, et voila enfin quel sera le repos, l'état permanent de la surface de notre globe. Car alors il y aura compensation entre les destructions et les réparations simultanées, et les montagnes sûrement ne s'abaisseront plus.»