Nothing is more evident, than that the general effect of mineral operations is to consolidate that which had been in an incoherent state when formed at the bottom of the sea, and thus to produce those rocks and indurated bodies which constitute the basis of our vegetable soil; but, that indurating or consolidating operation is not the immediate object of our observation; and, to see the evidence of that operation, or the nature of that cause, requires a long chain of reasoning from the most extensive physical principles. Our present subject of investigation requires no such abstract distant media, by which the effect is to be connected with its cause; the actual operation in general is the object of our immediate observation; and here we have only to reason from less to more, and not to homologate things which may, to men of narrow principles, appear to be of different kinds. But even here we find difficulty in persuading those who have taken unjust views of things; for, those who will not deny the truth of every step in this chain of reasoning, will deny the end to which it leads, merely because they are not disposed to admit the progress of that order which appears in nature.
In the last chapter, I have been using arguments to prove that M. de Luc has reasoned erroneously, in concluding the future stability of a continent; and I have been endeavouring to show that our continent is necessarily wasted in procuring food to plants, or in serving the various purposes of a system of living animals. We have now in view to illustrate this theory of the degradation of the surface of the earth; a theory necessarily leading to that system of the world in which a provision is made for future continents; and a theory explaining various natural appearances which otherwise are not to be understood. A door may thus be opened for the investigation of natural history, particularly that which traces back, from the present state of things, those operations of nature which are more immediately connected with what we take much pleasure to behold, viz. the surface of the earth stored with such a variety of beautiful plants, and inhabited by such a diversity of animals, all subservient to the use of man.
There are two ways in which we may look for the transactions of time past, in the present state of things, upon the surface of this earth, and read the operations of an ancient date in those which are daily transacted under our eye. The one of these is to examine the soil, and to trace the origin of that which we find loose upon the surface of the earth, or only compacted by the soft and cohesive nature of some of its materials. In thus studying the soil we shall learn the destruction of the solid parts; and though, by this means, we cannot form an estimate of the quantity of this destruction which had been made, we shall, upon many occasions, see a certain minimum of this quantity which may perhaps astonish us.
The second method here proposed, is to examine the solid part of the earth, in order to learn the quantity of matter which had been separated from this mass. Here also we shall not be able to compute the quantity of what had been destroyed; but we shall every where find a certain minimum of this quantity, which will give us an extensive view with regard to the operation of the elements and seasons upon the surface of this earth. We shall now examine more particularly those two ways of judging with regard to the operations of time past, and the changes which have been made upon the surface of our land, by those active causes, which, being in the constitution of this earth, must continue to operate with undiminished power, and tend to preserve the whole amidst the destruction of its particular parts.
The quality of the soil or travelled earth of the globe is various; because the solid parts, from the destruction of which the soil is formed, consist of very different substances, in the different portions of each country. Thus, in one part of a country, the soil will be calcareous, or containing much of that species of substance; in another, again, it will be argillaceous; in another sandy, where the prevailing substance is siliceous. These are the original soils; other substances may be considered as adventitious to this soil, though natural to the surface of the earth, which is covered with plants and animals. The substance of those animal and vegetable bodies, mixed with the soil, adds greater fertility to the earth, and gives a soil which is still more compounded in its nature, but still composed of those materials now enumerated.
We have been now supposing the solid parts below, or in the same field, as furnishing materials of which the soil is formed; this soil then partakes of the nature of those solid parts, whether more simple or more compound. There is, however, another subject of variety, or still greater composition in soils; this is the transportation of materials from a distance; and this, in general, is performed by the ablution of water, in following the declivity of the surface. But sand is sometimes travelled by the wind, and proceeds along the surface of the earth, without regard to the declivity, and changes the nature of soil in those places which happen to be exposed to this accident.
There cannot be any extensive, great, or distant travelling of sand or soil by means of the wind, except in those places which are sterile for want of rain, and thus are destitute of rivers and of streams; for, these running waters form every where a bar to this progressive movement of the soil, even if the sterility or dryness should permit the blowing of the sand. But the operation of streams and rivers, carrying soil and stones along the surface of the earth, is constant, great, and general over all the globe, so far as a superfluity of water, in the seasons of rain, falls upon the earth.
From the amazing quantity of those far travelled materials, which in many places are found upon the surface of the ground, we may with certainty conclude, that there has been a great consumption of the most hard and solid parts of the land; and therefore that there must necessarily have been a still much greater destruction of the more soft and tender substances, and the more light and subtile parts which, during those operations of water, had been floated away into the sea. This appears from the enormous quantities of stones and gravel which have been transported at distances that seem incredible, and deposited at heights above the present rivers, which renders the conveyance of those bodies altogether inconceivable by any natural operation, or impossible from the present shape of the surface. This therefore leads us to conclude, that the surface of the earth must have been greatly changed since the time of those deposits of certain foreign materials of the soil. Examples of this kind have been already given. I shall now give one from the Journal de Physique.
«Les bords du Rhône aux environs de Lyon, et sur la longueur de quarante lieues, et de plus, des montagnes entières, dans le même pays, sont formes de pierres dont on ne trouve les analogues que dans la Suisse. Ce fait presqu'incompréhensible est accompagné de beaucoup de circonstances qui méritent d'être détaillées dans un discours plus longue que celui-ci. Il y a cependant une que je ne peux pas m'empêcher de rapporter ici, comme une suite de ce que je viens de dire.
«Dans cette grand catastrophe, à laquelle j'attribue le transport de ces matières alpines, il se fit de grandes échancrures dans le Jura; les plus profondes que j'aie vues sont celles de Jougue de Sainte-Croix, du val de Mousthier Travers, de Someboz au val de Saint-Inver, une cinquième aux environs du village de Grange, trois lieues plus bas que Bienne, et une sixième à quatre à cinq lieues plus bas que Soleure, à l'endroit dit la cluse. Cette dernière est la plus profonde, et se trouve de niveau avec les eaux de l'Aar. Beaucoup de ces matières étrangères au Jura, ont passé par ces échancrures, et sans doute, par bien d'autres et se sont répandues, dans plusieurs de ces vallées. J'en ai vu un suite bien marquée qui a passé par Jougue, par Saint-Antoine, part Mont Perreux, les Grangettes, les Granges Friards, Oye, et qui est allée jusqu'aux plaines de Pontarlier. Cette suite est en ligne droite vis-à vis l'échancrure de Jougue, et la direction de la vallée qui est au bas de ce village. On en trouve quelques morceaux à Metabiefs, mais je n'en ai point vu aux Longevilles, ni à Roche-Jean. Il y en a au-dessus de Saint-Croix ou d'autres ont pu passer aussi pour aller de même aux environs de Portarlier. Il y en a dans le val de Mousthier-Travers jusqu'au dessus de village de Butte; elles ont même passé les roches de Saint-Sulpice du côté des Verrières de Suisse, ou l'on a été obligé d'en faire sauter de gros blocs avec de la poudre pour dégager la grande route; il y en a dans les vallées de Tavannes, et de Delemont; on en trouve bien plus loin, j'en ai vu près de Roulans, et je ne douterois pas que les pierres meulières de Moissez et des environs n'eussent la même origine.»