Theory of the Earth Volume Ii Part 4

The study of this subject must tend to enlarge the mind of man, in seeing what is past, and in foreseeing what must come to pa.s.s in time; and here is a subject in which we find an extensive field for investigation, and for pleasant satisfaction. The hideous mountains and precipitous rocks, which are so apt to inspire horror and discontentment in minds which look at sensible objects only for immediate pleasure, afford matter of the most instructive speculation to the philosopher, who studies the wisdom of nature through the medium of things. As, on the one hand, the summit of the mountain may be supposed the point of absolute sterility, so, on the other, the sandy desert, moved by nothing but the parching winds of continents distant from the sources of abundant rains, finishes the scale of natural fertility, which thus diminishes in the two opposite extremes of hot and dry, of cold and wet; thus is provided an indefinite variety of soils and climates for that diversity of living organised bodies with which the world is provided for the use of man. But, between those two extremes, of mountains covered with perpetual snow, and parched plains in which every living thing must perish, we find the most pleasant subject of contemplation, in studying the means employed in nature for producing the beautiful and benevolent system of hills and valleys, of fertile soils and well watered plains, of the most agreeable circ.u.mstances and proper situations for every thing that lives, and for the preservation of an indefinite variety of organised bodies which propagate their species.

Without this philosophic view of things, the prospect of the surface of this earth is far from giving always satisfaction or contentment to the mind of man, who is subject to be continually displeased with that which is presented to his view, and which, in his opinion, is not the best; in his partial views of things, it is either too high or too low, too cold or too warm, too moist or too dry, too stiff for the labour of his plough, or too loose for the growing of his corn. But, considering nature as the common parent of living growing propagating bodies, which require an indefinite variety of soils and climates, the philosopher finds the most benevolent purpose in the end proposed, or effect which is attained, and sees perfect wisdom in the effectual means which are employed. This is the view that I would wish men of science to take; and it is for this purpose that I am now to examine the phenomena of the surface of this earth.

If strata, formed at the bottom of the sea, had been consolidated by internal operations proper to the earth, and afterwards raised for the purpose of a habitable world; and if, for the purpose of vegetation, the solid land must be resolved into soil by the dissolution and separation of its parts, as is required in the theory, the strata, instead of being entire immediately below the soil, should be found in a mutilated state; the ends of hard and solid beds should present their fractures or abrupt sections immediately under the confused materials with which they are covered; and the softer strata should appear to suffer gradual resolution and decay, by which may be perceived their transition into soil, the most important part of all the operations of the globe which do not immediately concern our life.

These are facts which every person of observation has it in his power to verify; they are facts for which nothing further can be laid than that the thing is truly so; and they are facts from which the most important arguments might be formed, were any doubt to be entertained concerning the justness of the theory which has now been given.

The theory consists in this, that it is necessary to have a habitable country situated in the atmosphere, or above the surface of the sea.

It is difficult to say precisely what const.i.tutes a habitable country. A resting place out of the water suffices for such amphibious animals as, while they necessarily live in the atmosphere, feed in the sea. Man, more versatile in his nature than most animals, and more capable of adapting his manners to his circ.u.mstances, is even sometimes found subsisting in situations where the land affords him little more than it does the seal on which he feeds. The growth of terrestrial plants, however, seems necessary to the idea of a habitable country; and, for the growth of plants, there is required soil: Now, this is only to be procured by the resolution or decay of solid land.

We are not to consider the resolution of our land as being the effect of accident, while it is performed by the operations of the sun and atmosphere, by the alternate action of moisture and of drought, and by the casual operations of a river in a flood. Nothing is more steady than the resolution of our land; nothing rests upon more certain principles; and there is nothing which in science may be more easily investigated.

Calcareous, argillaceous, and other soluble earths, compose many of the strata; but in many more, which are partly or chiefly composed of insoluble substances, those soluble earths are mixed in various proportions. Now, when the siliceous substance, which is the insoluble part, shall be supposed resisting every effort of the elements towards its dissolution, those compound ma.s.ses upon the surface of the earth, however endued with hardness and solidity, are gradually impaired by the dissolution of some of their const.i.tuent parts, and by the separation of others which are thus exposed to the ablution of water. In like manner, by the resolution of the surrounding parts, the solid _silex_, which is supposed to be insoluble, is removed from its bed, and thus suffers new parts of the solid land to be exposed to those injuries of the air, by which the general good of plants, of animals, and even of future worlds, are consulted.

The solid land is resolved into stones, gravel, sand, earths, and clays; all or either of these, by retaining moisture, and affording places for the roots of plants, are disposed for vegetation in different degrees; a mixture of the different earths being, upon the whole, the best suited to that purpose; and this compound body, mixed with vegetable or animal substances, becoming a most luxuriant soil.

Soils are thus formed, either by the resolution of the surface of that land upon which they are to rest, or by the transportation of those solid parts to be again deposited upon another basis. In this manner soils are constantly changing upon the same spot; sometimes they are meliorated, at other times impoverished. From the tops of the mountains to the sh.o.r.es of the sea, all the soils are subject to be moved from their places, by the natural operations of the surface, and to be deposited in a lower situation; thus gradually proceeding from the mountain to the river, and from the river, step by step, into the sea.

Countries are thus formed at the mouths of rivers in the sea, so long as the quant.i.ties of materials transported from the land exceeds that which is carried from the sh.o.r.e, by tides and currents, into the deeper water.

The soil, with which the surface of this earth is always covered more or less, is extremely various, both with respect to quant.i.ty and quality; it is found resting upon the solid parts; and those solid parts are always more or less affected by the influences of the atmosphere near the surface of the earth. Those parts of the strata which approach the surface are always in a decayed state; and this sometimes may be observed for very considerable depths, according as the quality of the materials, and the situation of the place dispose to that effect. This general observation however may be formed, that, _cet. par._ the strata become always more solid, or are found in their sound and natural state, more and more in proportion as we sink into the earth, or have proceeded from the surface.

There is nothing of which we have more distinct experience than this, That, universally upon the surface of the earth, the solid parts are dissolving and always going into decay; whereas, at a sufficient depth below, they are found in their natural consolidated state. The operations of man in digging into the ground, as well as the sections of the earth so often formed by brooks and rivers, affords such ample testimony of this truth that nothing farther need be observed upon this head only that this is a most important operation in the natural economy of the globe, and forms a subject of the greatest consequence in the present Theory of the Earth, which holds for principle, that the strata are consolidated in the mineral regions far beyond reach of human observation.

Consistently with this view of things, the strata or regular solid parts, under the soil or travelled earth, should be found in some shape corresponding to the represented state of those things, when affected by the powers which have acted upon the surface of the earth. Here, accordingly, the strata are always to be observed with those marks of resolution, of fracture, and of separation, which have most evidently arisen from the joint operation of those several causes that have been now explained. But though every operation of the globe be necessarily required for the explanation of those appearances which we now examine, it is princ.i.p.ally the action of the sun and atmosphere, and the operations of the waters flooding the surface of the earth, that form the proper subject of the present investigation.

It must not be imagined that, from the present state of things, we may be always able to explain every particular appearance of this kind which occurs; for example, why upon an eminence, or the summit of a ridge of land which declines on every side, an enormous ma.s.s of travelled soil appears; or why in other places, where the immediate cause is equally unseen, the solid strata should be exposed almost naked to our view. We know the agents which nature has employed for those purposes; we know the operations in which the solid parts are rendered soil of various qualities and for different purposes; and when we find the marks of those natural operations in places where, according to the present circ.u.mstances, the proper agents could not have acted or existed, we are hereby constrained to believe, that the circ.u.mstances of those places have been changed, while the operations of nature are the same.

It is thus that we shall find reason to conclude an immense period of time, in those operations which are measured by the depradations of water acting upon the surface of the earth; a period however which is to be esteemed a little thing compared with that in which a continent had taken birth and gone into decay; but a period which interests us the more to examine, in that it approaches nearer to another period, for the estimation of which _some data_ may perhaps be found by naturalists and antiquaries, when their researches shall be turned to this subject. It is only in this manner that there is any reasonable prospect of forming some sort of calculation concerning that elapsed time in which the present earth was formed, a thing which from our present data we have considered as indefinite.

In this view which we are now taking of the surface of the earth, nothing is more interesting than the beds of rivers; these take winding courses around the hills which they cannot surmount; sometimes again they break through the barrier of rocks opposed to their current; thus making gaps in places by wearing away the solid rock over which they formerly had run upon a higher level; and thus leaving traces of their currents in the furrowed sides of rocky mountains, far from the course of any water at the present time.

So strongly has M. de Saussure been impressed with this and some other appearances, that he has imagined a current of water which, however in the possibility of things, is not in nature; and which moreover could not have produced the appearances now mentioned, which is the work of time, and the continued operation of a lesser cause. We are further obliged to him for the following facts.

Vol. 1. (page 163.) Les tranches nues et escarpees des grandes couches du pet.i.t et surtout du grande Saleve, presentent presque partout les traces les plus marquees du pa.s.sage des eaux, qui les ont rongees et excavees, on voit sur ces rochers, des sillons a peu pres horizontaux, plus ou moins larges et profonds; il a de 4 a 5 pieds de largeur, et d'une longueur double ou triple, sur 1 ou 2 pieds de profondeur. Tous ces sillons ont leur bords termines des courbures arrondies; telles que les eaux ont coutume de les tracer. Je dis qu'ils sont a peu pres horizontaux, parce qu'ils sont par fois inclines de quelques degres, en descendant vers le sud-sud-ouest, suivant la pente qu'a du avoir le courant. This is evidently the effect of a river running along the side of a rock of such soft materials as may be worn by the friction of sand and stones; and such are the materials of the rocks now considered.

Notwithstanding that it is so easy to explain this appearance by the operation of natural causes, M. de Saussure proceeds in taking it in another view. De tels filons ne sauroient avoir ete traces par les eaux des pluies; car celles-ci forment des excavations, ou perpendiculaires a l'horizon ou dirigees suivant la plus grande inclinaison des faces des rochers; au lieu que celles la font tracees presqu'horizontalement sur de faces tou-a-fait verticales. Here our author takes it for granted that things upon the surface of this earth were always the same as at present; and he reasons justly from these principles. But we are now tracing a former state of things; and those furrowed rocks testify the former current of a river by their side.

This operation of rivers undermining the sides of mountains, and causing scenes of ruin and destruction, may be ill.u.s.trated by what our author has described under the t.i.tle of _Ravage du temps sur les Rochers de Saleve_, --236. La ou ces couches manquent, il est aise de voir qu'elles ont ete detruites par le tems; les couches meme horizontales, contres lesquelles elles out appuyees, ont souffert en bien des endroits des alterations considerables.

Un peintre qui voudroit monter son imagination, et se faire des grandes idees des ravages du tems sur de grands objects, devroit aller au pied de Saleve, a l'extremite des ces grands rochers, au-dessus du coin, hameau fort eleve de la paroisse de Collonge.

On voit la des rochers tailles a pic a la hauteur de plusieurs centaines de pied avec des faces, ici planes et uniformes, la partagees et sillonnes par les eaux.

La base de ces rochers est couverte de debris et de fragmens enormes, confus.e.m.e.nt enta.s.ses; un de ces debris soutenu fortuitement par d'autres est demeure, et paroit de pres un obelisque quadrangulaire d'une hauteur prodigieuse; de plus loin on reconnoit que sa sommite est une arrete tranchante, et qu'il a la forme d'un coin; et c'est peut-etre cette forme qui a donne son nom au hameau qu'il domine.

L'Angle meme de la montagne est partage par une fente qui le traverse de part en part. Cette profonde fissure merite qu'on la voye, et meme qu'on la penetre. Elle est tortueuse, et dans quelques endroits si etroite, qu'a peine un homme peut il y pa.s.ser. Quand vous y etes engages vous trouvez des places ou les sinuosites du rocher vous cache le ciel, plus loin elles le laissent apercevoir par echappees; ailleurs vous voyez des blocs de rochers engages dans la creva.s.se, et suspendus au-dessus de votre tete.

In his route from Contamine to Bonneville, he observes, page 365, Enfin vis-a-vis la Bonne-ville, ces memes escarpemens des bases du mole, presentent une grande echancrure, qui paroit etre le vuide qu'a laisse une montagne qui s'est anciennement ecroulee; ses debris sont encore enta.s.ses au-dessous de l'echancrure. Il paroit meme qu'elle etoit plus elevee que ses voisines, j'en juge par leur couches qui montent a droite et a gauche, contre le vuide qu'elle a laisse.

-- 493. En suivant la route de servez, on voit sur sa gauche la continuation des rocs escarpes qui couronnent les montagnes situees au-dessus de Pa.s.sy. Un de ces rochers est si eleve, et en meme tems si mince que l'on a peine a concevoir qu'il puisse se tenir debout et resister aux orages.

C'est aupres de cette sommite elevee qu'etoit situee une montagne qui s'eboula en 1751, avec un fracas si epouvantable, et une poussiere si epaisse et si obscure, que bien de gens crurent que c'etoit la fin du monde.

Vitaliano Donati, who was sent from Turin to examine this phenomenon, says in his letter, which M. de Saussure transcribes, that the great snows, which fell that year in Savoy, increasing the operation of some lakes, the waters of which continually undermined this mountain, occasioned the fall of three millions of cubic toises of rock.

In describing the Saleve, our author proceeds to mention other appearances equally conclusive with regard to the operations of water, but such as may be found over all the surface of the globe, to have been brought about by natural causes. Ce que l'on nomme le Grottes de l'Hermitage, ou ces excavations profondes de 30 pieds, et 8 ou 10 fois aussi longues produites par la destruction totale de plusieurs couches de rocher.

La gorge meme de Monetier, ou cette grande echancrure qui separe le grand Saleve du pet.i.t, et dans le fond de laquelle est renferme le joli vallon de Monetier, paroit avoir ete formee par un courant semblable, qui descendant des Alpes par la vallee de l'Arve, venoit se jetter dans notre grand courant; car les couches correspondantes du grand et du pet.i.t Saleve indiquent leur ancienne jonction; et l'on ne comprend pas quel agent auroit pu detacher et emporter la piece enorme qui manque en cet endroit a la montagne.

Further, in treating of the changes made in the form of the Jura by the ravages of time, our author observes, page 273, vol. I.

Le faite de la montagne, battu de tous cotes par les vents, et par les pluies, a souffert des alterations les plus grandes: ici les couches du cote du lac ont ete detruites, et laissent voir les sommites des couches opposees, dont les escarpemens paroissent tourner contre ce meme lac; la, ce font les couches du cote de la vallee de Mijoux, qui out ete emportees, et la montagne en pente uniforme de notre cote, est escarpee du cote de celle vallee; plus loin, le faite entier a ete enleve, et la on voit des abaiss.e.m.e.ns ou des gorges comme aux Faucilles, a St. Serge, etc.

Les flancs et la base de La montagne ont aussi ete degrades par les torrens que produisent la pluie et les neiges fondues, qui ont forme de larges et profondes excavations.

These ravages of time, or rather of the wasting operations of the surface of the earth, however great, compared with the little changes that we find in our experience, or in the most ancient record of our histories, are little things, considering the softness and solubility of the materials, and compared with the wasting of the Alps, which we find in tracing up those same rivers to their sources in the icy valleys. Let us go up the Arve to the valley of Chamouni. From this fertile valley, M. de Saussure heads us up the Montanvert, 428 fathoms above the level of the valley, and consequently 954 above that of the sea.

From this mountain we descend again into the high frozen valley which runs between the granite mountains, and pours its ice into the valley of Chamouni.

In this high valley, which communicates with an immensity of the like kind, we find ourselves among the most hard and durable materials. Here we must perceive, that most enormous ma.s.ses of those solid materials had, in the course of time, been wasted by the flow effects of air and water, of the sun and frost, in order to hollow out those barren valleys of immense extent, which have, during an amazing tract of time, contributed from their solid rocks to the formation of travelled soils below, but which materials have long ago been travelling in the sea. The sides of those valleys are solid rock here exposed naked to our view. It is to such a place as this that we should go to see the operations of the surface wasting the solid body of the globe, and to read the unmeasurable course of time that must have flowed during those amazing operations which the vulgar do not see, and which the learned seem to see without wonder!

M. de Saussure, in his second volume of _Voyages dans les Alps_, has given us a most interesting view of this scene, p. 6.

En montant au Montanvert, on a toujours sous ses pieds la vue de la vallee de Chamouni, de l'Arve qui l'arrose dans toute la longueur, d'une soule de villages et de hameaux entoures d'arbres et de champs bien cultives. Au moment ou l'on arrive au Montanvert, la scene change; et au lieu de cette riante et fertile vallee, on se trouve presqu'au bord d'un precipice, dont le fond est une vallee beaucoup plus large et plus etendue, remplie de neige et de glace, et bordee de montagnes colossales, qui etonnent par leur hauteur et par leurs formes, et qui effraient par leur sterilite et leurs escarpements.

It is the cause of this appearance, of deep valleys and colossal mountains, that I would now wish my readers to perceive. This is a thought which seldom strikes the mind of wondering spectators, viewing those lofty objects; they are occupied with what they see, and do not think how little what they see may have been, compared with what had been removed in the gradual operations of the globe. We have but to suppose this scene hewn out of the solid ma.s.s of country raised above the level of the valley; and, that this had been the case, must appear from the examination of all around.

Let us follow our author up those valleys between the solid granite mountains, valleys which properly are great rivers of ice moving, grandly but slowly, the ruins of those mountains upon which they were gathered. It is the Glacier de Bois upon which he is set out, (p. 26.)

Apres une bonne demi-heure de marche sur le glacier, nous traversons une arrete de glace chargee de terre, de sable et de debris de rocher.

J'ai parle dans le 1er. vol. de ces arretes paralleles a la longueur de glaciers, que l'on voit souvent dans le milieu de leur largeur, ou a des distances plus ou moins grandes de leurs bords. J'ai fait voir qu'elles sont produites par des debris qui du haut des montagnes, roulent sur le glacier, et qui entraines par la glace sur laquelle ils reposent suivent comme elle une direction oblique en descendant tout-a-la-fois vers le milieu et vers le bas de la vallee.

Dix minutes apres, nous traversames une seconde arrete plus haute que la premiere, et nous jugeames que sous ces debris la glace etoit de 20 ou 25 pieds plus elevee que dans les endroits ou l'air et les rayons du soleil agissent librement sur elle. On rencontre une troisieme arrete a vingt minutes de la seconde, et la quatrieme, qui est la derniere, la suit de tres-pres.

Ici nous nous trouvons au point ou le glacier des bois se divise, comme je l'ai dit, -- 611, en deux grandes branches, dont l'une tourne a droite vers le Mont-Blanc, et prend le nom de glacier de _Tacul_, et l'autre a gauche se nomme le glacier de _Lechaud_. Il seroit, sans doute, plus interessant de suivre celle de la droite, et de s'approcher ainsi du Mont-Blanc; ses pentes de neige et de glace, qui se presentent a nous, semblent meme n'etre point absolument inaccessibles: mais ce sont des apparences trompeuses; des glaciers entrecoupes de profondes creva.s.ses masquees ca et la par des couches minces de neige les approches de cette redoutable montagne, quoique peut-etre en choisissant une annee ou il seroit tombe beaucoup de neige, et en prenant le temps ou cette neige seroit encore ferme, quelque cha.s.seur adroit et courageux pourroit tenter cette route.

Comme dans ce moment cette entreprise est absolument impraticable, nous suivons la branche gauche de la vallee, et apres deux heures de marche sur le glacier des bois, nous en sortons au pied de celui du Talefre, c'est-a-dire, a l'endroit ou celui-ci vient verser sa glace dans celui-la qui a change de nom, et qui s'appelle ici le _glacier de Lechaud_.

La vue du glacier du Talefre est ici majestueuse et terrible. Comme la pente par laquelle il descend est extremement rapide, les glacons se pressant mutuellement, se dressent, se relevent, et presentent des tours, des pyramides divers.e.m.e.nt inclinees, qui semblent pretes a ecraser le voyageur temeraire qui oseroit s'en approcher.

Pour parvenir au sommet de ce glacier, ou il est moins incline et par cela meme moins inegal, nous gravissons le rocher qui est a la gauche du cote du couchant. Ce rocher se nomme _le Couvercle_; il est domine par une cime inaccessible, qui, suivant l'usage du pays, est decoree du nom _aiguille_, et, en prenant le nom du glacier le plus proche, s'appelle _l'aiguille du Talefre_.

La pente, par laquelle on gravit le couvercle, est excessivement rapide; on suit une espece de sillon creuse dans le roc par la nature; quelques pointes de roc aux quelles on se cramponne, en montant avec les mains, autant et plus qu'avec les pieds, ont fait donner a ce pa.s.sage le nom _d'egralets_ ou de pet.i.ts degres. Ce pa.s.sage n'est cependant point dangereux, parce que le roc, qui est un granit tres-coherent, permet d'a.s.surer toujours solidement les mains et les pieds; mais la rapidite le rend un peu effrayant a la descente.

Lorsqu'on est au haut des egralets, on suite un pente beaucoup moins rapide; on marche tantot sur du gazon, tantot sur de grandes tables de granit, et on arrive ainsi au bord du plan du glacier du Talefre. On nomme le _plan_ d'un glacier la partie elevee et a-peu-pres horizontale dans laquelle on peut le traverser.

Nous avions mis une heure et un quart a monter du glacier de Lechaud au plan de celui du Talefre. Nous fumes tentes de nous reposer un moment avant d'entrer sur celui-ci. Tout nous invitoit a choisir cette place, un beau gazon arrose par un ruisseau qui sortoit de dessous la neige et qui rouloit son eau crystalline sur un sable argente, et ce qui etoit plus seduisant encore, une vue d'une etendue et d'une beaute dont une description ne peut donner qu'une bien foible idee.

-- 631. En effet comment peindre, a l'imagination des objets qui n'ont rien de commun avec tout ce que l'on voit dans le reste du monde; comment faire pa.s.ser dans l'ame du lecteur cette impression melee d'admiration et de terreur qu'inspirent ces immenses amas de glaces entoures et surmontes de ces rochers pyramidaux plus immenses encore; le contraste de la blancheur des neiges avec la couleur obscure des rochers, mouilles par les eaux que ces neiges distillent, la purete de l'air, eclat de la lumiere du soleil, qui donne a tous ces objets une nettete et une vivacite extraordinaires; le profond et majestueux silence qui regne dans ces vastes solitudes, silence qui n'est trouble que de loin en loin par le fracas de quelque grand rocher de granit ou de glace qui s'ecroule du haut de quelque montagne; et la nudite meme de ces rochers eleves, ou l'on ne decouvre ni animaux, ni arbustes, ni verdure. Et quand on se rappelle la belle vegetation, et les charmans paysages que l'on a vus le jours precedens dans le ba.s.ses vallees, on est tente de croire qu'on a ete subitement transporte dans un autre monde oublie par la nature, ou sur une comete dans son aphelie. La vue du Montanvert ne donne de celle-ci qu'une idee tres-imparfaite; la on ne voit qu'un seul glacier, au lieu que d'ici vous voyez les trois grands glaciers des Bois, de Lechaud et du Tacul, sans compter un grand nombre d'autres moins considerables qui, comme celui du Talefre, versent leurs glaces dans les glaciers princ.i.p.aux.