Theory of the Earth Volume Ii Part 13

9. De la pierre calcaire dans laquelle sont deposes des especes de noyaux oblongs, quelques fois par couches, mais sans suite, composes d'un sable fin de couleurs grisatre, plus blanc que la pierre calcaire, tres-durs, faisant feu au briquet, et sans effervescence avec les acides.

10. On retrouve encore des couches minces sablonneuses melees de parties calcaires.

11. D'autres de pierre calcaire compacte et d'une epaisseur considerable.

12. Alternativement de moins compactes. Dans l'une de ces couches il y a de la pyrite vitriolique decompose, qui teint en jaune les parties du rochers sur lesquels a flue la decomposition martiale.

13. Quelques filons de spath jaunatre, entremeles de veines de schiste pur, ne faisant pas effervescence.

14. De la pierre calcaire.

15. Des schistes meles de parties calcaires.

16. De la pierre calcaire pure.

17. De larges filons de spath calcaire jaunatre meles de quartz, faisant feu au briquet, et une peu d'effervescence.

18. De la pierre calcaire pure grise, plus foncee que dans le bas.

19. Des couches calcaires jaunatres.

20. Enfin tout le haut n'est que pierre calcaire grise et denaturee.

Cette partie superieure du monte est fort etendue. Tout ce qui est sur le local qui va en pente a.s.sez douce vers le milieu, n'a pas ete a.s.sujetti a de roulis et a des frottemens, il n'y a que la longueur du tems qui l'ait degrade, et lui ait imprime le caractere de la vetuste.

On ne voit que des pierres calcaires, elles sont remplies de trous, de fentes, et de creva.s.ses; beaucoup, paroissent poreuses comme de la la pierre ponce grossiere; le sejour des neiges des eaux, la gelee, et l'intemperie des saisons a tout fait. On voit de tous cotes que l'eau s'y infiltre et s'y perd. L'arrangement de cette espece de pierre par couches, facilite l'entree des eaux dans l'interieur de la montagne pour aller donner naissance a des sources, a des torrents, et quelquefois a d'a.s.sez fortes rivieres qui sortent du pied de ces montagnes calcaires; lors de la fonte des neiges, l'eau ne se verse point des sommets de ces sortes de montagnes comme de dessus les autres especes de rochers qui absorbent moins les eaux. Dans le milieu de ce haut il y a un pet.i.t lac d'un grand quart de lieue de long de forme ovale, ou se ra.s.semblent les eaux des neiges fondues; il n'y a point d'issues a ce lac, ses eaux sont absorbees, et se perdent dans l'interieur de la montagne; il n'y avoit que peu de glace alors sur ce lac, mais il y avoit encore beaucoup de neiges aux environs; un glacier est sur la droite, se prolonge et va fermer le sommet du vallon ou est Loiche; c'est le meme glacier qu'on appercoit derriere les sources chaudes. Deux aiguilles de rocher en cone, fort hautes s'elevent au-dessus du sommet; elles sont toujours couvertes de neiges: leur ressemblance et leur proximite a donne le nom de Gemmi Jumeaux, a cette montagne--On voit a ses pieds a une profondeur immense le village de Loiche, qui paroit etre tout au pied du rocher; il faut cependant une grand heure et demie pour s'y rendre, tant la hauteur diminue le point de perspective. Le chemin qui est pratique dans ce rocher, y a ete par-tout taille; il le contourne certains endroits, dans d'autres il est creuse de facon qu'il forme une voute couverte, et qu'on a le rocher suspendu au-dessus de soi. Il est rare de trouver l'occasion de pouvoir examiner de detailler avec autant de facilite une montagne d'une pareille hauteur. A compter des galleries jusqu'aux glaciers de la Gemmi, ces rochers perpendiculaires et a pic ont plus de trois lieues d'etendue; ils diminuent en hauteur a mesure que le pays s'eleve, et se confond dans les plus hautes alpes, qui sont surmontees d'autre ma.s.ses de rochers.

De l'autre cote du vallon, et vis-a-vis des montagnes qui forment celles de la Gemmi, est la montagne du midi, separee par la Dala, torrent qui vient du glacier a la tete du vallon, dont les eaux paroissent avoir creuse le lit etroit et profond. Cette montagne est calcaire comme la Gemmi, et paroit en avoir fait partie: je n'ai pu verifier nulle part si elle etoit posee sur des schistes: tout est dans un grand boulevers.e.m.e.nt sur sa pente qui est fort rapide. A environs trois quarts de lieue des bains, un sentier fort difficile, qui pa.s.se sur les decombres de cette montagne et dans des bois de sapins fort obscurs, conduit par un pente fort rapide a un rocher perpendiculaire, comme sont presque tous ceux du canton on y trouve des ech.e.l.les appuyees contre; on parvient a la premiere, en grimpant par les avances et les saillies du rocher; d'autres roches facilitent le moyen d'arriver a la seconde; on trouve ainsi sept ech.e.l.les dont quelques-unes sont fort hautes, et par lesquelles on se guide au sommet de ce rocher; on est bien surpris d'y trouver un terrain en pente, ou il y a des champs laboures et des vignes qui entourent le village d'Albinien, dont les habitans ont place ces ech.e.l.les pour raccourcir le chemin qui conduit a Loiche, ou ils vont vendre leurs denrees.

Nous quittons les bains de Loiche pour nous rapprocher du Rhone: on repa.s.se par Inden, on ne trouve ensuite que des pierres, des rochers, des escarpemens; c'est un chemin des plus mauvais jusqu'au bourg de Loiche; c'est pour eviter ce chemin qu'on a fait celui des galleries. Le bourg de Leuck, ou Loiche, est un des princ.i.p.aux endroits du Vallais, bati en pierres, dans une position fort elevee et tres-forte; l'art avoit encore ajoute anciennement a la force de son a.s.siette, il y a encore d'anciens forts et des tours; toute cette hauteur est calcaire; on a la plus belle vue de ce lieu, elle s'etend sur tout le bas Vallais jusqu'au dela de Martigny; nous avons donne une foible idee de cette vue, avant d'arriver aux bains de Loiche, car les expressions manquent pour rendre ces grands tableaux. Un spectacle bien interessant pour ceux qui etudient les changemens qui arrivent journellement a la surface du globe, est la vue du Kolebesch, montagne fort elevee en face du bourg de Leuck, et de l'autre cote du Rhone; cette montagne est calcaire ainsi que la chaine sur la rive gauche du Rhone, du moins la partie avancee qui forme le vallon ou coule ce fleuve. Des chutes, des eboulemens y ont produit de grands changemens; les eaux et les torrens qui viennent des parties elevees, ont entraine ces debris, les ont deposes aux pieds de la montagne, et en ont forme une colline qui a plus d'une demie-lieue jusqu'au Rhone, et plus d'une grande lieue de large, en forme circulaire; elle s'etend vers le haut et le bas Vallais; la partie superieure est couverte de pres et des paturages; celle du cote du bas Vallais est couverte d'une foret; elle va en pente douce; la grosseur des arbres prouve combien la formation de ce terrain est ancienne.

Depuis la consolidation de ce terrain des torrens nouveaux y ont creuse un ravin large et profond, par lequel s'ecoulent actuellement les eaux des montagnes, et les pierres qu'elles en arrachent. Le Rhone mine et emporte le pied de cette colline qui resserroit son cours, avec ces materiaux il va plus loin former des atterriss.e.m.e.ns composes des matieres les plus pesantes; les parties les plus fines le limon suspendu dans ces eaux servent ensuite a couvrir les anciens atterriss.e.m.e.ns, au moyen desquels ils deviennent susceptibles de toute espece de vegetation; ses eaux finissent de s'epurer dans le lac Leman, d'ou il sort clair et limpide, ainsi que toutes les rivieres qui sortent des lacs jusqu'a ce que d'autre torrens, tombant des montagnes, viennent les troubler de nouveau.

Here is a most satisfactory view of the structure of this country on each side of the Rhone; strata of lime-stone and schisti, almost horizontal or little inclined, compose the mountains from their most lofty summits to the deepest bottom of those valleys. Such mountains cannot have been formed in any other manner than by the waste and degradation of their horizontal strata; consequently, here we are certain, that, from the summit of the Gemmi to those upon the other side of the Rhone, all the solid substance had been hollowed out by water.

Thus were formed the valleys of the Rhone, the Dala, and a mult.i.tude of others.

M. de Saussure has given us a description of a tract of alpine country of the same kind with that of the _Vallais_ now considered, so far as the strata are here in a horizontal position, instead of that highly inclined situation in which those primary bodies are commonly found. It is the description of Mount-Rosa Journal de Physique, Juillet 1790.

Here the same interesting observation may be made with regard to the immense destruction which must necessarily have taken place, in the elevated ma.s.s of solid earth, by the dissolving or wearing power of running water; and this will be clearly explained by the formation of those mountains and valleys, which, while they correspond with mountains and valleys in general, have something particular that distinguishes them from most of the Alps, where the strata, being much inclined, give occasion to form ranges of peaks disposed in lines according to the directions of the inclined strata. Here on the contrary, there being no general inclination of the strata to direct the formation of the peaks, they are found without any such order. I shall give it in M. de Saussure's own words.

En effect toutes les hautes sommites que j'avois observees jusqu'a ce jour sont ou isolees comme l'Etna, ou rangees sur des lignes droites comme le Mont-Blanc et ses cimes collaterales. Mais la je voyois le Mont Rose compose d'une suite non-interrompue de pics gigantesques presqu'egaux entr'eux, former un vaste cirque et renfermer dans leur enceinte, le village de Macugnaga, ses hameaux, ses paturages, les glaciers qui les bordent, et les pentes escarpees qui s'elevent jusqu'aux cimes de ces majestueux colosses.

Mais ce n'est pas seulement la singularite de cette forme qui rend cette montagne remarquable; c'est peut-etre plus encore sa structure.

J'ai constate que le Mont-Blanc et tous les hauts sommets de sa chaine sont composes de couches verticales. Au Mont-Rose jusqu'aux cimes les plus elevees, tout est horizontal ou incline au plus de 30 degres.

Enfin il se distingue encore par la matiere dont il est construit. Il n'est point de granits en ma.s.se, comme le Mont-Blanc et les hautes cimes qui l'entourent; ce sont des granits veines et des roches feuilletees de differens genre qui const.i.tuent la ma.s.se entiere de cet a.s.semblages de montagnes, depuis bases jusqu'a ses plus hautes cimes. Ce n'est pas que l'on n'y trouve du granit en ma.s.ses, mais il y est purement accidentel, et sous la forme de rognons, de filons, ou de couches interposees entre celles des roches feuilletees.

On ne dira donc plus que les granits veines, le _gneiss_ et les autres roches de ce genre, ne sont que les debris des granits ra.s.sembles et agglutines au pied des hautes montagnes, puisque voila des roches de ce genre dont la hauteur egale a tres-peu-pres celle des cimes granitiques les plus hautes connues, et ou l'on ferois bien embarra.s.se a trouver la place des montagnes de granit dont les debris out pu leur servir de materiaux; sur-tout si l'on considere la ma.s.se enorme de l'ensemble des murs d'un cirque tel que celui du Mont-Rose. En effet, ce seroit une hypothese inadmissible que de supposer, qu'anciennement il a existe dans le vuide actuel du cirque une montagne de granit, et que ce cirque est le produit des debris de cette montagne. Car comment ne resteroit-il aucun vestige de cette montagne? On concoit bien que sa tete auroit pu se detruire, mais son corps, la base du moins, protegee par les debris de sa tete acc.u.mules autour d'elle qu'est ce qui auroit pu l'aneantir; d'ailleurs les parois interieures du cirque quoique tres-escarpees ne sont pourtant pas verticale; elles s'avancent de tous cotes vers l'interieur; et le fond, le milieu meme du cirque n'est point du granit, il est de la meme nature que ses bords. Enfin nous avons reconnu que les montagnes qui forment la couronne du Mont-Rose se prolongent au dehors a de grandes distances en sorte que leur ensemble forme une ma.s.se incomparablement plus grande que celle qui auroit rempli le vuide interieur du cirque.

Il faut donc reconnoitre, comme tous les phenomenes le demontrent d'ailleurs, qu'il existe de montagnes de roches feuilletees, composees des memes elemens que le granit, et qui sont sorties comme lui des mains de la nature sans avoir commence par etres elles-memes des granits[22].

[Footnote 22: M. de Saussure, upon the evidence before us, might have gone farther, and maintained that the ma.s.ses of granite, which here traverse the strata in form of veins and irregular blocks, had been truly of a posterior formation. But this is a subject which we shall have afterwards to consider in a particular manner; and then this example must be recollected.]

Here is an example the most interesting that can be imagined. Those mountains are the highest in Europe, and their lofty peaks are altogether inaccessible upon one side. They had all been formed of the same horizontal strata. How then have they become separated peaks? And how have the valleys been hollowed out of this immense ma.s.s of elevated country?--No otherwise than as we may perceive it, upon every mountain, and after every flood. It is not often indeed, that, in those alpine regions, any considerable tract of country is to be found, where an example so convincing is exhibited. It is more common for those mountains of primary strata or schistus to rise up in ridges, which, though divided into great pyramids, may still be perceived as connected in the direction of their erected strata. These last, although affording the most satisfactory view of that mineral operation by which land, formed and consolidated at the bottom of the sea, had been elevated and displaced, are not so proper to inform us of the amazing waste of those extremely consolidated bodies, as are those where the strata have preserved their original horizontal portion. It is in this last case, that there are data remaining for calculating the _minimum_ of the waste that must have been made of those mountains, by the regular and long continued operations of the atmospheric elements upon the surface of this earth.

It is the singularity of these horizontal strata in that extensive alpine ma.s.s, which seems to have engaged M. de Saussure, who has inspected so much of those instructive countries, to make a tour around those mountains, and to give us a particular description of this interesting place. Now, from this description, it is evident, that there is an immense ma.s.s of primary or alpine strata nearly in the horizontal position, which is common to all the strata at their original formation; that this horizontal ma.s.s had been raised into the highest place of land upon this globe; and that, in this high situation, it has suffered the greatest degradation, in being wasted by the hand of time, or operations of the elements employed in forming soil for plants, and procuring fertility for the use of animals. Here is nothing but a truth that may almost every where be perceived; but here that important truth is to be perceived on so great a scale, as to enable us to enlarge our ideas with regard to the natural operations of this earth, and to overcome those prejudices which contracted views of nature, and magnified opinions of the experience of man may have begotten,--prejudices that are apt to make us shut our eyes against the cleared light of reason.

Abundant more examples of this kind, were it necessary, might be given, both from this very good observator, and from M. de Luc[23].

[Footnote 23: Vid. Discours sur l'Histoire Naturelle de la Suisse, pa.s.sim; _but more particularly under the article of Route du Grindle_ wald a meiringen _dans le pays de Hasti:_ Also Hist: de la Terre, Lettre 30. p. 45, et Lettre 31. page 68, etc.]

I will now only mention one from this last author, which we find in the Journal de Physique, Juin 1792.

Entre Francfort et Hanau, le mein est borde sur ses deux rives, de collines dans lesquelles la _lave_ se trouve encha.s.see entre des _couches calcaires_. Ces _couches_ sont tres-remarquables par leur contenue, qui est le meme au-dessus et au-dessous de la _lave_, et qu'on retrouve dans les _couches_ d'une grande etendue de pays, ou, comme d'ordinaire, on voit leurs sections abruptes dans les flancs de collines, mais sans _lave_, excepte dans le lieu indique.

The particular structure of those lime-stone strata, with the body of basaltes or subterraneous lava which is interposed among them, shows evidently the former connection of those two banks of the river, by solid matter, the same as that which we see left there, and in the flanks of those hills. That which is wanting, therefore, of those stratified ma.s.ses, in that great extent of country, marks out to us the minimum of what has been lost, in having been worn by the attrition of travelled materials.

I would now beg leave, for a moment, to transport my reader to the other side of the Atlantic, in order to perceive if the same system of rivers wearing mountains is to be found in that new world, as we have found it in the old.

Of all the mountains upon the earth, so far as we are informed by our maps, none seem to be so regularly disposed as are the ridges of the Virginian mountains. There is in that country a rectilinear continuity of mountains, and a parallelism among the ridges, no where else to be observed, at least not in such a great degree.

At neither end of those parallel ridges is there a direct conveyance for the waters to the sea. At the south end, the Allegany ridge runs across the other parallel ridges, and shuts up the pa.s.sage of the water in that direction. On the north, again, the parallel ridges terminate in great irregularity. The water therefore, that is collected from the parallel valley, is gathered into two great rivers, which break through those ridges, no doubt at the most convenient places, forming two great gapes in the _blue ridge_, which is the most easterly of those parallel ridges.

Now, so far as mountains are in the original const.i.tution of a country, the ridges of those mountains must have been a directing cause to the rivers. But so far as rivers, in their course from the higher to the lower country, move bodies with the force of their rolling waters, and wear away the solid strata of the earth, we must consider rivers as also forming mountains, at least as forming the valleys which are co-relative in what is termed _mountain_. Nothing is more evident than the operation of those two causes in this mountainous country of Virginia; the original ridges of mountains, or indurated and elevated land, have directed the courses of the rivers, and the running of those rivers have modified the mountains from whence their origin is taken. I have often admired, in the map, that wonderful regularity with which those mountains are laid down, and I have much wished for a sight of that gap, through which the rivers, gathered in the long valleys of those mountains, break through the ridge and find a pa.s.sage to the sea.

A description of this gap we have by Mr Jefferson, in his notes on Virginia.

The pa.s.sage of the Potomac, through the Blue Ridge, is perhaps one of the most stupendous scenes in nature. You stand on a very high point of land. On your right comes up the Shenandoah, having ranged, along the foot of the mountains, an hundred miles to seek a vent. On the left approaches the Potomac, in quest of a pa.s.sage also. In the moment of their junction, they rush together against the mountain, rend it asunder, and pa.s.s off to the sea.

The first glance of this scene hurries our senses into the opinion, that this earth had been erected in time; that the mountains were formed first; that the rivers began to flow afterwards; that in this place particularly they have been dammed up by the Blue Ridge of mountains, and have formed an ocean which filled the whole valley; that, continuing to rise, they have at length broken over this spot, and have torn the mountain down from its summit to its base. The piles of rock on each hand, but particularly on the Shenandoah, the evident marks of this disrupture and avulsion from their beds, by the most powerful agents of nature, corroborate the impression. But the distant finishing which nature has given to the picture is of a different character. It is a true contrast to the foreground. It is as placid and delightful as that is wild and tremendous. For the mountain being cloven asunder, she presents to your eye, through the cleft, a small catch of smooth blue horizon at an infinite distance in the plain country, inviting you, as it were, from the riot and tumult roaring around, to pa.s.s through the breach, and partake of the calm below. Here the eye ultimately composes itself; and that way too the road happens actually to lead. You cross the Potomac above the junction, pa.s.s along its side through the base of the mountain for three miles, its terrible precipices hanging in fragments over you, and within about twenty miles reach of Frederick town, and the fine country around it. This scene is worth a voyage across the Atlantic. Yet here, as in the neighbourhood of the natural bridge, are people who have pa.s.sed their lives within half a dozen of miles, and have never been to survey these monuments of a war between the rivers and mountains, which must have shaken the earth itself to its center.

To this description of the pa.s.sage of the Potomac may be added what Mr Jefferson, in the appendix, has given from his friend Mr Thomson, secretary of Congress.

The reflections I was led into on viewing this pa.s.sage of the Potomac through the Blue Ridge were, that this country must have suffered some violent convulsion, and that the face of it must have been changed from what it probably was some centuries ago; that broken and ragged faces of the mountain on each side of the river; the tremendous rocks which are left with one end fixed in the precipice, and the other jutting out, and seemingly ready to fall for want of support; the bed of the river for several miles below obstructed, and filled with the loose stones carried from this mound; in short, every thing on which you cast your eye evidently demonstrates a disrupture and breach in the mountain, and that before this happened, what is now a fruitful vale, was formerly a great lake, or collection of water, which possibly might have here formed a mighty cascade, or had its vent to the ocean by the Susquehanna, where the Blue Ridge seems to terminate. Besides this, there are other parts of this country which bear evident traces of a like convulsion. From the best accounts I have been able to obtain, the place where the Delaware now flows through the Kittatinny mountain, which is a continuation of what is called the North Ridge, or mountain, was not its original course, but that it pa.s.sed through what is now called the Wind-gap, a place several miles to the westward, and above an hundred feet higher than the present bed of the river. This Wind-gap is about a mile broad, and the stones in it such as seem to have been washed for ages by water running over them. Should this have been the case, there must have been a lake behind that mountain; and, by some uncommon swell in the waters, or by some convulsion of nature, the river must have opened its way through a different part of the mountain, and meeting there with less obstruction, carried away with it the opposing mounds of earth, and deluged the country below with the immense collection of waters to which this new pa.s.sage gave vent. There are still remaining, and daily discovered, innumerable instances of such a deluge on both sides of the river, after it pa.s.sed the hills above the falls of Trenton, and reached the champaign. On the New Jersey side, which is flatter than the Pennsylvania side, all the country below Croswick hills seems to have been overflowed to the distance of from ten to fifteen miles back from the river, and to have acquired a new soil, by the earth and clay brought down and mixed with the native sand. The spot on which Philadelphia stands evidently appears to be made ground. The different strata through which they pa.s.s in digging for water, the acorns, leaves, and sometimes branches which are found above twenty feet below the surface, all seem to demonstrate this.

How little reason there is to ascribe to extraordinary convulsions the excavations which are made by water upon the surface of the earth, will appear most evidently from the examination of that natural bridge of which mention is made above, and which is situated in the same ridge of mountains, far to the south, upon a branch of James's River. Mr Jefferson gives the following account of it.

"The natural bridge, the most sublime of nature's works, is on the ascent of a hill, which seems to have been cloven through its length by some great convulsion. The fissure, just at the bridge, is by some admeasurements 270 feet deep, by others 205; it is about 45 feet wide at the bottom, and 90 feet at the top; this of course determines the length of the bridge, and its height from the water. Its breadth in the middle is about 60 feet, but more at the ends; and the thickness of the ma.s.s at the summit of the arch about 40 feet. A part of its thickness is const.i.tuted by a coat of earth, which gives growth to many large trees. The residue, with the hill on both sides, is one solid rock of lime-stone. The arch approaches the semi-elliptical form; but the larger axis of the ellipsis, which would be the cord of the arch, is many times longer than the transverse. Though the sides of the bridge are provided in some parts with a parapet of fixed rock, yet few men have resolution to walk to them, and look over into the abyss. You involuntarily fall on your hands and feet, and creep to the parapet, and look over it. Looking down from this height about a minute gave me a violent headache. If the view from the top be painful and intolerable, that from below is delightful in the extreme. It is impossible for the emotions arising from the sublime to be felt beyond what they are here. On the sight of so beautiful an arch, so elevated, so light, and springing as it were up to heaven, the rapture of the spectator is really indescribable!

The fissure, continuing narrow, deep, and straight, for a considerable distance above and below the bridge, opens a short but very pleasing view of the north mountain on one side, and blue ridge on the other, at the distance each of them of about five miles. This bridge is in the county of Rockbridge, to which it has given name, and affords a public and commodious pa.s.sage over a valley, which cannot be crossed elsewhere for a considerable distance. The stream pa.s.sing under it is called Cedar Creek: it is a water of James's River, and sufficient in the driest seasons to turn a grist mill, though its fountain is not more than two miles above[24]."

[Footnote 24: Upon this occasion it may be observed, the most wonderful thing, with regard to cosmology, is that such remnants, forming bridges, are so rare; this therefore must be an extraordinary piece of solid rock, or some very peculiar circ.u.mstances must have concurred to preserve this monument of the former situation of things.]

Thus both in what is called the Old World and the New, we shall be astonished in looking into the operations of time employing water to move the solid ma.s.ses from their places, and to change the face of nature, on the earth, without defacing nature. At all times there is a terraqueous globe, for the use of plants and animals; at all times there is upon the surface of the earth dry land and moving water, although the particular shape and situation of those things fluctuate, and are not permanent as are the laws of nature.

It is therefore most reasonable, from what appears, to conclude, that the tops of the mountains have been in time past much degraded by the decay of rocks, or by the natural operations of the elements upon the surface of the earth; that the present mountains are parts which either from their situation had been less exposed to those injuries of what is called time, or from the solidity of their const.i.tution have been able to resist them better; and that the present valleys, or hollows between the mountains, have been formed in wasting the rock and in washing away the soil.

If this is the case, that rivers have every where run upon higher levels than those in which we find them flowing at the present, there must be every where to an observing eye marks left upon the sides of rivers, by which it may be judged if this conclusion be true. I shall now transcribe a description of a part of the _Vallais_ by which this will appear. (Discours sur l'Histoire Naturelle de la Suisse.)

Apres avoir pa.s.se le village de Saint-Leonard, on commence a monter la montagne de la Platiere; cette route est on ne peut plus interessante pour le naturaliste Etc.

On se trouve fort eleve au-dessus du Rhone quand on est sur le haut de ce chemin, dont on decouvre un de plus singuliers, des plus riches, et de plus varies pa.s.sages qu'on puisse imaginer. On voit sous ses pieds le Rhone serpenter dans le lit qu'il se creuse actuellement, car il change et tout prouve qu'il en a souvent change; une quant.i.te prodigieuse de pet.i.tes isles le separent et le coupent en une mult.i.tude de canaux et de bras; ces isles sont couvertes les unes d'arbres, d'arbustes, de paturages, de bosquets et de verdure, d'autres de pierres, de sable, et de debris de rochers; quelques-unes sont formees ou occasionnees par un amas de troncs d'arbres enta.s.ses avec de grands sapins renverses dont les long tiges herissees de branches droites et nues representent des chevaux de frise, et donnent l'idee de ces abatis destines a preserver un pays contre l'approche de l'ennemi. Du cote du bas Vallais, on suit a perte de vue le fleuve dans ses sinuosites et ses detours, on l'appercoit egalement dans le haut Vallais; des avances de montagne le cachent quelquefois: il reparoit et diminue insensiblement en approchant de ces monts eleves ou il prend sa source: le fond du vallon paroit etre de niveau, s'abaisser seulement d'une pente douce du cote du bas Vallais: des mamelons, des hauteurs des monticules isoles, quelquefois groupes de differentes manieres, sont repandus dans cet es.p.a.ce, et rappellent la vue d'une pre devaste par les taupes; plusieurs de ces hauteurs sont surmontees des ruines d'antiques chateaux, d'eglises, et de chapelles; des villages distribues ca et la enrichissent ce fond, qui d'ailleurs est couvert de paturages, de champs d'arbres, de bois, et de bosquets; les enclos des possessions le coupent en mille figure bizarres et irregulieres. Ces monticules avec leurs fabriques s'elevent au-dessus de tous ces objets varies; quelques-unes se distinguent par leur cotes ecroules qui sont a pic; la blancheur de ces eboulemens contraste singulierement avec les verts qui sont les couleurs dominantes du vallon. Au-de-la des coteaux, des montagnes s'elevent et vont s'appuyer et s'adosser a ces ma.s.ses, a ces colosses enormes de rochers a pic eleves comme des murailles et d'une hauteur prodigieuse qui forment cette barriere qui separe le Vallais de la Savoie. Les contours du pied de ces monts forment des entrees de vallons et de vallees d'ou descendent et se precipitent des torrens qui viennent grossir les eaux du Rhone; la vue cherche a penetrer et a s'etendre dans ces es.p.a.ces, l'imagination cherche vainement des pa.s.sages dans effrayantes limites, parmi ces ecueils et ces rochers amonceles, elle est arretee partout; de noires forets de sapin sont suspendues parmi ces rochers blancs-jaunatres, qui se terminent enfin par une mult.i.tude d'aiguilles et de pyramides qu'on voit percer au travers des neiges et des glaces, s'elancer dans les nues, s'y cacher et s'y perdre.

En examinant de plus pres ces mamelons repandus dans le vallon, on voit qu'ils sont composes de pierres, de sables, et de debris rapportes et amonceles sans ordre depuis des temps dont rien ne peut fixer l'epoque: on voit que les eaux du Rhone ont coule a leurs pied, qu'il en a mine plusieurs et a occasionne leurs chutes et leurs ruines. On voit actuellement quelques mamelons qui subissent ces memes degradations, et fournissent au Rhone les materiaux dont il va former plus loin ces atteriss.e.m.e.ns dont nous avons parle. La confusion et le desordre qui se remarque dans la composition interieure de ces mamelons prouvent qu'ils ne sont pas le produit de la mer ou des eaux qui ont travaille successivement et lentement a la formation de la plupart des terrains; mais que le fond de ce vallon a ete rempli des decombres et des debris des montagnes superieures, qu'ils y ont ete entraines par des inondations et des debordemens subits; que les eaux du Rhone ensuite ont parcouru ce vallon qu'il a souvent change de lit; que c'est en tournant et en circulant dans ce terrain nouvellement forme, qu'il a creuse les es.p.a.ces qui sont entre ces mamelons, et que c'est en creusant le terrain qu'ils se sont eleves; leurs formes et leurs pentes allongees vers le bas Vallais, sont de nouvelles preuves que ce sont les eaux actuelles qui ont change la surface de ce terrain, nous verrons de nouvelles preuves de ce que nous disons en avancant d'avantage vers le haut Vallais; il n'y a peut-etre point d'endroit plus propre a etudier le travail des eaux que ce vallon qu'on a la facilite de voir et d'examiner sous des aspects differentes.