Theory of the Earth Volume Ii Part 7

For, all the land of the present earth being a certain composition of materials, perfectly similar to such as would result from the gradual destruction of a continent in the operations of the inhabited world, this composition of our land could not be explained without having recourse to preternatural means, were there not in the const.i.tution of this earth an active cause necessarily, in the course of time, destroying continents.

It is therefore of great importance to this Theory, to show, that the land is naturally wasted, though with the utmost economy; and that the continents of this earth must be in time destroyed. It is of importance to the happiness of man, to find consummate wisdom in the const.i.tution of this earth, by which things are so contrived that nothing is wanting, in the bountiful provision of nature, for the pleasure and propagation of created beings; more particularly of those who live in order to know their happiness, and who know their happiness on purpose to see the bountiful source from whence it flows.

We are to conceive the continent of the earth, when first produced above the surface of the ocean, to be in general consolidated, with regard to its structure, by the same mineral operations which are necessarily employed in raising it from its primary situation at the bottom of the sea, to that in which we now inhabit it.

We are now to consider the purpose of this mineral body, exposed to the influences of the atmosphere, that so we may see the intention of its solid composition, as well as that of its resolution, or natural solubility when thus exposed; and we are to trace the ultimate effects of this order of action in the economy of the globe, that so we may perceive the wisdom of nature perpetuating the system of a living world in an endless succession, of changing perishable forms.

The purpose of the land of this earth, in being placed above the sea and immersed in the atmosphere, is to sustain a system of plants and animals. But; for the purpose of plants; there is required a soil; and, as there is in the vegetable system a vast variety of plants with different habits or natural const.i.tutions, there is also required a diversity of soils, in which those vegetable bodies are to be made to live and prosper. From the bare rock exposed to the sun and wind, to the tender mud immersed in water, there is a series to be observed; and in every stage or step of this gradation, there are plants adapted to those various soils or situations. Therefore nothing short of that diversity of soils and situations, which we find upon the surface of the earth, could fulfill the purpose of nature, in producing a system of vegetables endued with such a diversity of forms and habits.

The soil or surface of this earth is no more properly contrived for the life and sustenance of plants, than are those plants for that diversity of animals, which will thus appear to be the peculiar care of nature in forming a world. Scarce a plant perhaps that has not its peculiar animal which feeds upon its various productions; scarce an animal that has not its peculiar tribe of plants on which the economy of its life, its pleasure, or its prosperity must depend.

If we shall suppose the continent of our earth to be a solid rock, on which the rain might fall, and the wind and waves might dash perpetually, without impairing its ma.s.s or changing its const.i.tution, what an imperfect world would we have! how ill adapted to the preservation of animal and vegetable life! But the opposite extreme would equally frustrate the intention of nature, in producing bounteously for the various demands of that multiplicity of species which the author of this world has thought proper to produce.

For if, instead of a solid rock, we shall suppose a continent composed of either dry sand or watery mud, without solidity or stability, how imperfect still would be that world for the purpose of sustaining lofty trees and affording fruitful soils!

We have now mentioned the two extreme states of things; but the const.i.tution of this earth is no other than an indefinite number of soils and situations, placed between those two extremes, and graduating from the one extreme, in which some species of animals and plants delight in finding their prosperity, to the other, in which another species, which would perish in the first, are made to grow luxuriantly.

That is to say, the surface of this earth, which is so widely adapted to the purpose of an extensive system of vegetating bodies and breathing animals, must consist of a gradation from solid rock to tender earth, from watery soil to dry situations; all this is requisite, and nothing short of this can fulfil the purpose of that world which we actually see.

We have been representing this continent of our earth as coming out of the ocean a solid ma.s.s, which surely it is in general, or in a great degree; but we find the surface of this body at present in a very different state; and now it will be proper to take a view of this change from solid rock to fertile soil.

Upon this occasion I shall give the description of nature from the writings of a philosopher who has particularly studied this subject. It is true that M. de Luc, who furnishes the description, draws, from this process of nature, an argument for the perpetual duration or stability of mountains; and this is the very opposite of that view which I have taken of the subject; but as, in this operation of nature producing plants on stones, he allows the surface of the solid stone to be changed into earth and vegetables, it is indifferent to the present theory how he shall employ this earth and vegetable substance, provided it be acknowledged that there is a change from the solid state of rock to the loose or tender nature of an earth, from the state of a body immovable by the floods and impenetrable to the roots of plants, to one in which some part of the body may be penetrated and removed.

[8]Les pluies et les rosees forment partout ou elles sejournent, des depots qui sont la premiere source de toute _vegetation_. Ces depots sont toujours meles des s.e.m.e.nces des _mousses_, que l'air charie continuellement, et auxquelles se joignent bientot les s.e.m.e.nces presque aussi abondantes des _gramens_, qui sont l'herbe dominante de nos prairies. Ainsi partout ou la pluie a forme quelque pet.i.t depot, il croit de la mousse ou des _gramens_. Ceux-ci demandent un peu plus de _terre vegetale_ pour croitre, ils germent, et se conservent princ.i.p.alement dans les intervalles et les creux des pierres: mais la _mousse_ croit bientot sur la surface la plus unie. Il n'est aucune pierre long-temps exposee a l'air, qui soit parfaitement polie; l'action de l'air, du soleil, des eaux, des gelees, detruiroit ce poli quand il existeroit. Le moindre creux alors recoit un depot de la pluie, et nourrit un brin de _mousse,_ ces brins poussent des racines; et de nouveaux jets autour d'eux, qui contribuent a arreter l'eau de la pluie et de la rosee, et par ce moyen a arreter les depots Nourriciers.

[Footnote 8: Histoire de la Terre, Tom. 2. page 26.]

Quand la mousse a multiplie ses filets, les depots s'augmentent plus rapidement encore; les brins de la _mousse,_ en sechant et pourrissant, en forment eux-memes; car leur substance n'etoit que ces memes depots faconnes: d'autres s.e.m.e.nces charriees par l'air, qui au-paravant glissaient sur les pierres, parce que rien ne les retenoit, tombent dans le fond de la _mousse_, et y trouvent l'humidite necessaire pour produire leurs premieres racines: celles-ci s'entrela.s.sent dans la _mousse_, ou elles se conservent a l'abri du soleil, et sont alors autant de pet.i.tes bouches qui pompent les sucs, que l'air, les pluies, et les rosees y deposent. Ces premieres plantes sont foibles, quelque fois meme elles ne parviennent pas a leur perfection: mais elles ont contribue a fixer la _terre vegetable_. En sechant et se decomposant, elles se transforment en cette _terre_, qui tombe au fond de la _mousse_, et qui prepare ainsi de la nourriture pour de nouvelles plantes qui alors prosperent et fructifient.

Nous connoissons peu encore ce que c'est que cette _terre vegetable_, ce depot des pluies ou en general de l'air. Cependant, en ra.s.semblant les phenomenes, on peut conjecturer, que la plupart des corps terrestres sont susceptibles d'etre changes en cette substance, et qu'il ne s'agit pour cette transformation que de les decomposer. J'entends par la une telle division de leurs parties, que devenant presque des elemens, elles puissent etre intimement melees a l'eau, et pompees avec elle par les tuyaux capillaires des plantes. En un mot, il semble suffisant qu'une matiere puisse entrer en circulation dans les vegetaux, pour qu'elle serve a en developper le tissu, et qu'elle y prenne la figure et les qualites que chacun de ces laboratoires est propres a produire.

Nous pouvons accelerer de bien des manieres la transformation des matieres terrestres en _terre vegetable_. La fermentation, la calcination, une plus grande exposition a l'air, differens melanges, rendent propres a la vegetation, des matieres qui ne l'etoient par elles-memes: voila ce que peuvent nos soins. Mais l'air travaille sans cesse et en mille manieres. Son simple frottement sur tous les corps, en enleve des particules si attenuees que nous ne les reconnoissons plus.

La _poussiere_ de nos appartemens en est peut-etre un exemple. De quelque nature que soient les corps dont elle se detache, c'est une poudre grisatre qui semble etre partout la meme. La formation de la _terre vegetable_ a probablement quelque rapport a celle-la. Toute la surface de la terre, les rocs les plus durs, les sables et les graviers les plus arides, les metaux meme, eprouvent l'action _rongeante_ de l'air et leurs particules attenuees, decomposees, recomposees de mille manieres, sont probablement la source princ.i.p.al de la vegetation.

_L'air_ lui-meme ainsi que _l'eau_, s'y combinent: beaucoup d'observations et d'experiences nous prouvent que ces deux fluides fournissent leur propre substance aux parties solides des vegetaux, et par consequent a la _terre vegetable_ qui les produit et qu'ils deposent. Quant.i.te de plantes se nourrissent de _l'eau_ seule, et nous laissant cependant en se sechant, un residu de matiere solide permanente. _L'air_ aussi se _fixe_ dans les corps terrestres, il fait partie de leur substance solide; les chimistes savent de plus en plus, et le _fixer_, et lui redonner son elasticite primitive, par divers procedes: et avant la mult.i.tude d'experiences qui se sont de nos jours sur cet objet interessant de la physique, le Dr. Hales avoit montre, que les vegetaux renferment une tres-grande quant.i.te _d'air_, qui s'y trouve sans ressort et comme matiere const.i.tuante.

Voila donc probablement les sources ou la nature puise peu a peu la _terre vegetable_ dont elle recouvre la surface de nos continens. Ce sont les particules, peut-etre, de tous les corps tant solides que fluides, extraites ou fixees par des procedes qui les rapprochent de leurs premiers elemens, et leur font prendre a nos yeux une meme apparence. Ces particules sont ainsi rendues propres a circuler dans les s.e.m.e.nces des plantes, a en etendre le tissu a y prendre toutes les proprietes qui caracterisent chaque espece, et a les conserver tant que la plante existe. Ces memes particules, apres la destruction des plantes, prennent le caractere general de _terre vegetable_, c'est-a-dire de provision toute faite pour la vegetation.

Les plus pet.i.ts recoins des montagnes, qui peuvent arreter l'eau de la pluie, sont certainement fertilises; ce ne sont pas seulement les grandes surfaces plates, ni les pentes; ce sont meme les faces escarpees des rochers les plus durs. S'il s'y fait quelque creva.s.se, un arbre s'y etablit bientot; et souvent il contribue, par l'accroiss.e.m.e.nt de ses racines, a accelerer la chute du lambeau de rocher qui l'avoit recu.

S'il y a quelque pet.i.te terra.s.se, ou seulement quelque partie saillante grande comme la main, elle est bientot gazonnee. Les plus pet.i.tes sinuosites se peuplent de plantes; et les surfaces les plus unies, celles memes qui sont tournees vers la bas, recoivent au moins quelqu'une de ces _mousses_ plates, nommes _lichen_ par les botanistes, qui ne font en apparence que pa.s.ser une couleur sur la pierre. Mais cette couche est ecaillee, et elle loge bientot de pet.i.tes plantes dans ses replis; de celles qui veulent l'ardeur du soleil, si le rocher est au midi, ou la fraicheur de l'ombre, s'il est au nord: c'est sur ces rochers en un mot, qui paroissent nues aux spectateurs ordinaires, que se trouve la plus grande variete de ces pet.i.tes plantes, qui font les delices des botanistes, et l'une des sources les plus abondantes ou la medicine puise les secours reels qu'elle fournit a l'humanite.

Quelle richesse dans les ressources de la nature! La pesanteur n'est pas plus prete a entrainer les pierres qui se detachent des montagnes, que l'air a fournir de s.e.m.e.nces celles qui se fixent: et des qu'une fois elles sont recouvertes de plantes, elles sont certainement fixees pour toujours, du moins contre les injures de l'air. Le fait meme nous l'annonce. Si ces ravins ou ces terreins quelconques, tendoient encore a rouler ou a se degrader, en un mot a se detruire de quelque maniere que ce fut, ils ne le recouvriroient, ni de _mousses_ ni d'aucune autre plante. La premiere vegetation est due a quelque depot de _terre vegetable_; et les pluies ou l'air n'en forment que lentement; le moindre mouvement la detruite. Le terrein est donc bien certainement fixe quand il se recouvre de plantes; et s'il s'y acc.u.mule de la _terre vegetable_, c'est un signe bien evident que rien ne l'attaque plus: car elle seroit la premiere emportee si quelque cause exterieure tendoit a detruire le sol qui la porte.

The doctrine here laid down by our author consists in this; first, That there is a genus of plants calculated to grow upon rocks or stones; those hard bodies then decay, in decomposing themselves, and affording sustenance to the plants which they sustain. Secondly, That by this dissolution of those rocks, and the acc.u.mulation of those vegetable bodies, there is soil prepared for the nurture and propagation of another genus of plants, by which the surface of the earth, naturally barren, is to be fertilised. It is also in this natural progress of things that the solid parts of the globe come to be wasted in the operations of the surface, and that lofty rocks are levelled, in always tending to bring the uneven surface of the earth to a slope of vegetating or fertile soil.

Here we are to distinguish carefully between the facts described by this author, who has seen so much of nature, and the conclusion which he would draw from his principles. The surface of most stones are dissolved, or corroded by the air and moisture. This gives lodgement to the roots of plants, which grow, die, and decay; and these are carried away with the earthy parts of the solid stone, in order to form a vegetable soil for larger plants, growing upon some bottom or resting place to which that earth is carried. Here is so far the purpose of rocks, to sustain a genus of plants which are contrived to live upon that soil; and here is so far a purpose for certain plants, in decomposing rocks to form a soil for other plants which have been made upon a larger scale, and are adapted to the use of man, the ultimate in the view of nature.

Our author concludes thus: (p. 37.) Le tems ne fera qu'augmenter l'epaisseur de la couche de _terre vegetable_ qui couvre les montagnes, et qui les garant.i.t ainsi de plus en plus de cette destruction a laquelle on les croit exposes: les pluies en un mot, au lieu de les degrader comme on se l'imagine y acc.u.muleront leurs depots. Tel est l'agent simple qu'employe si admirablement le Createur pour la conservation de son ouvrage.

Such, indeed, is the admirable contrivance of the system, that, in the works of nature, nothing shall be destroyed more than is necessary for the preservation of the whole. But, that the whole is preserved by the necessary destruction of every individual body, and the change of every part which comes within the examination of our senses, is sufficiently evident to require no farther ill.u.s.tration in this place, where we are contemplating the destruction of the strongest things, by means the most effectual, though really slow, and apparently most feeble.

In his 30th letter, this author describes the progress of nature, in bringing precipitous rocks to that slope and covering of soil which is to maintain plants of every kind, and to establish woods. (P. 40.) J'ai l'honneur d'exposer a V.M. les causes qui garantissent de destruction exterieure les terreins sur lesquels la _pesanteur_ ne peut plus agir que pour les consolider. Mais ce n'est pas ainsi que sont actuellement la plupart de nos montagnes; il en est peu qui soyent deja parvenus a cet etat permanent. Tout roc nud est attaque par l'air et les meteores, et il tend a se detruire quelle que soit sa durete. Mais ce seroit peu que cette destruction exterieure; elle pourroit meme cesser enfin totalement par l'effet seul des _mousses_, s'il n'y avoit pas des causes plus puissantes qui pendant quelque tems agissent dans l'interieur.

Il n'est presque point de rocher qui offre a l'air une seule ma.s.se compacte; ils sont ou creva.s.ses, ou formes par couches; et l'eau s'insinue toujours dans ces fentes. Quand cette eau vient a se geler, elle agit comme un coin pour ecarter les pieces entre lesquelles elle se trouve. V.M. seroit etonnee de la grandeur des ma.s.ses que cette cause peut mouvoir: elle agit exactement comme la poudre a canon dans les mines; detachant toutes les pieces exterieures qui commencent a se separer, et en decouvrant ainsi de nouvelles. Chaque hiver renouvelle donc la surface de certains rochers, ou facilite l'ouvrage pour les hivers suivans.

Plusieurs autres causes agissent encore pour separer les rochers deja creva.s.ses, qui se trouvent a l'exterieur des faces escarpees. Le pet.i.t moellon qui s'y acc.u.mule, les depots des pluies, les plantes qui y croissent, les alternatives de l'humidite et de la secheresse, les vicissitudes de la chaleur, les vents meme, sont autant de causes continuellement agissantes quand la _pesanteur_ les seconde. Les rochers escarpes se detruisent donc par de continuels eboulemens.

Mais toutes ces matieres qui tombent, ne sont pas perdues pour les montagnes; il s'en perd meme bien peu. Elles s'arretent au pied des rochers dont elles sont successivement detachees; et la elles s'enta.s.sent, s'elevant en forme de _talus_ contre ces rochers eux-memes.

If the solid body of the Alps, the most consolidated ma.s.ses of our land, is thus reduced to the state of soil upon the surface of the earth contrived for the use of plants, _a fortiori_, softer bodies, less elevated and less consolidated ma.s.ses, will be considered as easily arriving at the purpose for which the surface of the earth has been intended. We only wish now to see the ultimate effect that necessarily follows from this progress of things; and how, in this course of nature, the land must end, however long protracted shall be the duration of this body, and however much economy may be perceived in this gradual waste of land;--a waste which by no means is so slow as not to be perceived by men reasoning in science; although scientific men, either reasoning for the purpose of a system which they had devised, or, deceived by the apparent state of things which truly change, may not acknowledge the necessary consequence of what they had perceived.

Let us now suppose all the solid ma.s.s of land, contained in our continent, to be transformed into soil and vegetable earth, it must be evident that no covering of plants, or interlacing of vegetable fibres, could protect this ma.s.s of loose or incoherent materials from the ravages of floods, so long as rivers flowed, nor from being swallowed by the ocean, so long as there were winds and tides. From the border of the land upon the sh.o.r.e, to the middle of the ocean, there is either at present an equable declivity at the bottom of the sea, or every thing tends to form this declivity, in gradually moving bodies along this bottom. But, however gradual the declivity of the bottom, or however slow the progress of loose materials from the sh.o.r.e towards the deepest bottom of the sea, so long as there are moving powers for those materials, they must have a progress to that end; the law of gravitation, always active, must prevail, and sooner or later the moving sea must swallow up the land.

But, along the borders of our continent, and in the courses of our rivers, there are rocks; these must be surmounted or destroyed, before the parts which they protect can be delivered up to the influence of those moving powers which tend to form a level; and we may be a.s.sured that those bulwarks waste. The bare inspection of our rocky coasts and rivers will satisfy the enlightened observator of this truth; and to endeavour to prove this to a person who has not principles by which to reason upon the subject, or to one who has false principles, by which he would create perpetual stability to decaying things, would be but labour lost.

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 ma.s.s 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 s.p.a.ce 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 const.i.tution 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'adouciss.e.m.e.nt des pentes arrete d'abord l'effet de ces deux grandes causes causes de destruction de montagnes, la _pesanteur_ et les _eaux_: la vegetation ensuite arrete l'effet de toutes les pet.i.tes 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].

[Footnote 9: This also would appear to be a part of that wise system of nature, in which nothing is done in vain, and in which every thing tends to accomplish the end with the greatest marks of economy and benevolence. Had it been otherwise, and the demolis.h.i.+ng powers of the land increased, in a growing rate with the diminution of the height, the changes of this earth and renovation of our continent, in which occasionally animal life must suffer, would necessarily require to be often repeated; and, in that case, chaos and confusion would seem to be introduced into that system which at present appears to be established with such order and economy that man suspects not any change; it requires the views of scientific men to perceive that things are not at present such as they were created; it requires all the observation of a natural philosopher to know that in this earth there had been change, although it is not every natural philosopher that observes the benevolence accompanying this const.i.tution of things which must subsist in change.]

The slope which our author gives to his mountains, in order to secure them from the ravages of time, is that which, according to his own reasoning, renders them fertile and proper for the culture of man; but fertile soil yields always something to the floods to carry away; and, while any thing is carried from the soil, the land must waste, although it may not then waste at the rate of those within the valleys of the Alps. According to the doctrine of this author, our mountains of Tweeddale and Tiviotdale, being all covered with vegetation, are arrived at that period in the course of things when they should be permanent.

But is it really so? Do they never waste? Look at the rivers in a flood;--if these run clear, this philosopher has reasoned right, and I have lost my argument. Our clearest streams run muddy in a flood. The great causes, therefore, for the degradation of mountains never stop as long as there is water to run; although, as the heights of mountains diminish, the progress of their diminution may be more and more r.e.t.a.r.ded.

Let us now see how far our author has reasoned justly with regard to vegetation, which, he says, stops the effects of all the little causes of destruction; this is the more necessary, as, in the present theory, it is the little causes, long continued, which are considered as bringing about the greatest changes of the earth.

Along the courses of our rivers there are plains between the mountains of greater or lesser extent; these are almost always fertile, and generally cultivated when large; when small, they are in pasture. The origin of these fertile soils, and their perpetual change, is to be described with a view to show, that vegetation, although most powerful in stopping the ravages of water, and for acc.u.mulating soil retained by this means, does it only for a time; after which the soil is again abandoned to the ravages of the running water, when no more protected by the vegetation.

Let us suppose the river running upon the one side of the haugh (which is the name we gave those little fertile plains) and close by the side of the mountain. In this case the bed of the river is deepest at the side of the mountain, which it undermines, leaving a falling _(un eboulement)_ on that side; on the other side, the river shelves gradually from the plain, and leaves soil in its bottom or stony bed upon the side of the haugh, in proportion as it makes advances in carrying away the bank at the bottom of the sloping mountain. The part which vegetation takes in this operation is now to be considered.

When the river has enlarged its bed by preying upon one side, whether of the mountain or the haugh, the water only covers it in a flood; at other times, it leaves it dry. Here, among the rocks and stones, the feeds of plants, left by the water or blown by the wind, spring up and grow; and, in little floods, some sand and mud is left among those plants; this encourages the growth of other plants, which more and more retain the fertile spoils of the river in its floods. At last, this bed of the river is covered perfectly with plants, which having retained plenty of fertile soil, although still rooted among the stones, opposes to the river a resistance which its greatest velocity is not able to overcome.

In this state, the haugh is always deepening or increasing its soil, and has its surface heightened. At last, when this soil becomes so high as only to be flooded now and then, it becomes most fertile, as the heavier parts are carried in the bed of the river, and the lighter soil deposited upon the plain. The operations of the river, upon the plain, thus increase at the same time the height and fertility of the haugh.

But this operation, of acc.u.mulated soil upon the stony bottom, has a period, at which time the river must return again upon its steps, and sweep away the haugh which it had formed. This is the natural course of things; and it happens necessarily from the deepening of the soil. Let us then examine this operation.

When no more soil is left upon the stony bottom than is sufficient for the covering of the ground, and rooting of plants which are also fixed in the solid ground or bottom of the soil, the water is not able to carry away the plants; and these plants protect the surface of loose soil. When again there is a depth of soil acc.u.mulated upon the haugh, the surface only is protected by the vegetable covering. But what avails it to the soil to be protected from above, when undermined by the enemy!

The vegetable roots now no longer reaching to the bottom where solidity is found, the tender soil below is easily washed away by the continued efforts of the stream; and the unsupported meadow, with the impregnable texture of its leaves, its roots, and its fibres, falls ruinously into the river, and is born away in triumph by the flood. The water thus reclaims its long deserted bed,--only in order to pa.s.s from it again, and circulate or meander from hill to hill in varying perpetually its course.

Now this progress of the river, or this changing of its bed, is determined by the strong resistance of the new made haugh, humbly standing firm in the protection of its vegetation, while the elevated surface of the older haugh, deserted by the inferior soil which it had ceased to protect, falls a victim to its exalted state, and pa.s.ses away to aggrandize another. This is the fate of haughs or plains erected by the operations of a river, and again destroyed in the natural course of things, or in the very continuation of that active cause by which they had been formed.

The water is constantly carrying the moveable soil from the higher to the lower place; vegetation often disputes the possession of these spoils of ruined mountains for a while; but, in the end, this vegetable protector, not only delivers up to the destroying cause the mineral soil which it had preserved, but, by its buoyancy in water, it facilitates the transportation of the stony parts to which this fibrous body is attached. Over and over a thousand times may be repeated this alternate possession of the transferable soil, by moving water on the one part and by fixed vegetation on the other, but at last all must land upon the sh.o.r.e, whether the river tends. Thus the mountain and the plain, the vegetable earth and the plants produced in that soil, must all return into the sea from whence either they themselves or their materials had come. In proportion as the mountains are diminished, the haugh or plain between them grows more wide, and also on a lower level; but, while there is a river running in a plain, and floods produced in the seasons of rain, there can be nothing stable in this const.i.tution of things evidently founded upon change.

The description now given is from the rivers of this country, where it is not unfrequent to see relicts of three or four different haughs which had occupied the same spot of ground upon different levels, consequently which had been formed and destroyed at different periods of time. But the same operation is transacted every where; it is seen upon the plains of Indostan, as in the haughs of Scotland; the Ganges operates upon its banks, and is employed in changing its bed continually as well as the Tweed[10]. The great city of Babylon was built upon the haugh of a river.

What is become of that city? nothing remains,--even the place, on which it stood, is not known.

[Footnote 10: An Account of the Ganges and Burrampooter Rivers, by James Rennel, Esquire. Philosophical Transactions, 1781.]