But to put this question out of doubt, with regard to this very valley of the river Doire, M de Saussure has given us the following decisive fact, § 881: «Immédiatement au-dessus de cette source, est un rocher qui répond si précisément à un autre rocher de la même nature, situé de l'autre côté de la vallée de Courmayeur, qu'on ne sauroit douter qu'ils n'aient été anciennement unis par une montagne intermédiaire, détruite par les ravages du temps.»
Now, to see how little the situation of the strata influences the shape of the valleys, I shall transcribe the two paragraphs immediately following that which has given occasion to the present discussion.
«Un peu au-dela de Nux, la vallée cesse d'être large et plane, comme elle étoit dans le environs de la cité; elle devient étroite et très variée; là stérile et sauvage, ici couverte de vergers et de prairies arrosées par la Doire.
«§ 961. Les couches des montagnes à notre gauche, qui depuis la cité avoient constamment couru à l'est et monté au nord, paroissent changer à un quart de lieue du village de Chambaise, qui est à une lieue et un quart de Nux. Elles montent d'abord au sud-est, et peu plus loin droit au sud, tandis que l'autre côté de la vallée elles paroissent monter à l'est.»
In every mountain, and in every valley, the solid parts below have contributed in some manner to determine the shape of the surface of the earth; but in no place is the original shape of the earth, such as it had first appeared above the sea, to be found. Every part of the land is wasted; even the tops of the mountains, over which no floods of water run, are degraded. But this wasting operation, which affects the solid rock upon the summit of the mountain, operates slowly in some places, compared with that which may be observed in others. Now, it is in the valleys that this operation is so perceptible; and it is in the valley that there is such a quick succession of things as must strike the mind of any diligent observer; but this is the reason why we must conclude, that at least all the valleys are the operation of running water in the course of time. If this is granted, we have but to consider the mountains as formed by the hollowing out of the valleys, and the valleys as hollowed out by the attrition of hard materials coming from the mountains. Here is the explanation of the general appearance of mountain and valley, of hill and dale, of height and hollow; while each particular shape must have its dependence, consequently its explanation, upon some local circumstance.
But, besides the general conformation of mountains and valleys, there may be also, in the forms of mountains, certain characters depending upon the species of substances or rocks of which they are composed, and the general manner in which those masses are wasted by the operations of the surface. Thus there is some character in the external appearance of a hill, a mountain, or a ridge of hills and mountains; but this appearance is generally attended with various circumstances, or is so complicated in its nature, as to be always difficult to read; and it is but seldom that it affords any very particular information; although, after knowing all the state and circumstances of the case, I have always found the appearances most intelligible, and strictly corresponding with the general principle of atmospheric influence acting upon the particular structure of the earth below.
M. de Saussure has given us an observation of this kind, in describing the mountains through which the Rhône has made its way out of the Alps, at the bottom of the Vallée.
«§. 1061. Plus loin le village de Juviana ou Envionne on voit des rochers qui ont une forme que je nomme moutonnée; car on est tenté de donner des noms à des modifications qui n'en ont pas, et qui ont pourtant un caractère propre. Les montagnes que je désigne par cette expression sont composées d'un assemblage de têtes arrondies, couvertes quelquefois de bois, mais plus souvent d'herbes, ou tout au plus de brousailles. Ces rondeurs contiguës et répétées forment en grand l'effet d'une toison bien fournie, ou de ces perruques que l'on nommé aussi moutonnées. Les montagnes qui se présentent sous cette forme, sont presque toujours de rochers primitives, ou au moins des stéatites; car je n'ai jamais vu aucune montagne de pierre à chaux ou d'ardoise revêtir cette apparence. Les signes qui peuvent donner quelque indice de la nature des montagnes, à de grandes distances et au travers des plantes qui le couvrent, sont en petit nombre, et méritent d'être étudiés et consacrés par des termes propres.»
When philosophers propose vague theories of the earth, theories which contain no principle for investigating either the general disorder of strata or the particular form of mountains, such theories can receive no confirmation from the examination of the earth, nor can they afford any rule by which the phenomena in question might be explained. This is not the case when a theory presents both the efficient and final cause of those disorders in bodies which had been originally formed regular, and which shows the use as well as means for the formation of our mountains. Here illustration and confirmation of the theory may be found in the examination of nature; and natural appearances may receive that explanation which the generalization of a proper theory affords.
The particular forms of mountains depend upon the compound operation of two very different causes. One of these consists in those mineral operations by which the strata of the earth are consolidated and displaced, or disordered in the production of land above the sea; the other again consists in those meteorological operations by which this earth is rendered a habitable world. In the one operation, loose materials are united, for the purpose of resisting the dissolving powers which act upon the surface of the earth; in the other, consolidated masses are again dissolved, for the purpose of serving vegetation and entertaining animal life. But, in fulfilling those purposes of a habitable earth, or serving that great end, the land above the level of the sea is wasted, and the materials are transported to the bottom of the ocean from whence that consolidated land had come. At present we only want to see the cause of those particular shapes which are found among the most elevated places of our earth, those places upon which the wasting powers of the surface act with greatest energy or force.