In proportion as the solid bulwark is destroyed, so is the soil which had been protected by it; and, in proportion as the solid parts of the mass of land are exposed to the influences of the atmosphere and water, by the ablution of the soil, more soil is prepared for the growth of plants, and more earth is detached from the solid rock, to form deep soils upon the surface of the earth, and to establish fertile countries at the mouths of rivers, even in making encroachment on the space allotted for the sea. But this production of land, in augmentation of our coasts, is only made by the destruction of the higher country. While, therefore, we allow that there is any augmentation made to the coast, or any earthy matter travelling in our rivers, the land above the coast cannot be stable, nor the constitution of our earth fixed in a state which has no tendency to be removed. M. de Luc, in his Histoire de la Terre, would make the mountains last for ever, after they have come to a certain slope. He sums up his reasoning upon this subject in these words: «L'adoucissement des pentes arrête d'abord l'effet de ces deux grandes causes causes de destruction de montagnes, la _pesanteur_ et les _eaux_: la végétation ensuite arrêté l'effet de toutes les petites cause.» If all the great and little causes of demolition are arrested by the slope of mountains and the growth of plants, the surface of the earth might then remain without any farther change; and this would be a fact in opposition to the present theory, which represents the surface of the earth as constantly tending to decay, for the purpose of vegetation, and as being only preserved from a quick destruction by the solid rocks protecting, from the ravages of the floods and sea, the loose materials of the land. It will therefore be proper to show, that this author's argument does not go to prove his proposition in the terms which he has given it, which is, that those sloped mountains are to last for ever, but only that these causes, which he has so well described, make the destruction of the mountains become more slow[9].