Theory of the Earth Volume Ii Part 18

L'etude de la montagne Santa-Venere, et des pays circonvoisins, m'apprit que ce volcan s'etoit eleve au milieu de la mer qui alors occupoit nos continens, que sa tete seule s'etoit soulevee au-dessus du niveau des eaux. Je fus convaincu que, lorsqu'il repandoit autour de lui des torrens de matieres enflammees, la mer enta.s.soit des depots calcaires; que chaque nouvelle eruption trouvoit un sol plus eleve, sur lequel elle se repandoit; que bientot les nouvelles matieres volcaniques etoient ensevelies sous de nouveaux depots, et qu'ainsi, par l'enta.s.s.e.m.e.nt successif et regulier des produit du feu et des depots de l'eau, s'etoit forme un enorme ma.s.sif, a sommet aplati et horizontal. Ce ma.s.sif occupoit tout le centre du Val di Noto, recouvroit de plusieurs centaines de toises le sol sur lequel s'etoit repandu les premieres laves, et fut divise, morcele et degrade par les courans ou par le ballottement des eaux, lors de la grande debacle du de la catastrophe qui changea l'emplacement des mers. Les vallons et les gorges qui se formerent au milieu de ce ma.s.sis, separerent les laves de la montagne a qui elles appartenoient, couperent les courans, et faconnerent, avec les debris de ce ma.s.sif des montagnes de toutes les formes, mais la majeure partie conique, ainsi qu'on peut le voir journellement, lorsque, dans un terrain argilleux et submerge l'eau, se retirant avec precipitation, excave par-tout ou elles trouve moins de resistance, creuse les premiers sillons qu'elle a traces et forme des pet.i.ts cones, dont les sommets sont a la hauteur du sol sur lequel reposoient les eaux. Les parties ou les laves avoient coule successivement dans la meme direction, les unes au-dessus des autres, ont donne naissance aux montagnes dans lesquelles les couches volcaniques et calcaires se succedent parallelement. Celles sur lesquelles aucunes laves ne se sont portees, n'ont produit que des montagnes totalement calcaires que se trouvent entremelees avec les autres. Celles enfin sur lesquelles le hazard ou des circonstances locales out enta.s.se de preference, et dans le meme lieu, les matieres que vomissoit le volcan, sans laisser le temps au depot des eaux de se meler avec elles, ont produit quelques pet.i.tes montagnes presque entierement volcanique, ou les cendres sont agglutinees par une pate calcaire, etc. Cette theorie rend raison de tous le phenomenes et de toutes les singularites qui s'observent dans le melange des produits du feu et des depots de l'eau, et une infinite de preuves de differens genres, mais qui seroient etrangeres a ce Memoire, concourent a demontrer, l'existence d'un ancien plateau qui etoit eleve de plusieurs centaines de toises au-dessus du sol actuel des vallees et du niveau de la mer, qui couvroit non seulement le Val _di Noto_, mais encore toute la Sicile, et dont les debris ont forme toutes les montagnes actuellement existantes, a l'exception de l'Etna.

It is not the explanation here given by the Chevalier de Dolomieu, of the manner in which this great ma.s.s of land was formed in the sea, that is concerned with the subject at present under our examination, but certain facts set forth in the Memoir, and a certain conclusion which is there endeavoured to be drawn from those interesting facts[28]. This will be understood by considering; first, it is on all hands acknowledged, that the stratified matter of the globe was successively deposited in the bottom of the sea; secondly, it is also agreed, that this great ma.s.s of Sicily, formed originally under the sea, was afterwards placed in the atmosphere, whether by the retreat of the sea or by the elevation of the land; and now, lastly, we are of one mind with respect to the present shape of things, as having been produced by the wasting away of great part of that ma.s.s which had been once continued all over the island, as high at least as the tops of the mountains, _i.e._ about a mile above the level of the sea; we only differ in the time and agents which have been employed in this Operation.

[Footnote 28: In the first part of this work, the distinction has been made of true volcanic productions, and those which are so frequently confounded with them; these last, though the creatures of subterranean fire, and bodies which have been made to flow in a fluid state, are clearly different from those ma.s.ses of lava which have issued from a volcano, as has been there described. I would only here observe, that, according to this Theory, these bodies, which the Chevalier de Dolomieu here represented as lava and volcanic production, must be considered as unerupted lavas, which had been made to flow among the strata of the earth, where other at the bottom of the sea, or during those operations by which this land was erected above the level of the ocean.]

On the one hand, the Memoir now before us represents this great effect as belonging to an unknown cause, so far as we are ignorant of that grand _debacle_ or _catastrophe_ which changed the situation of the sea.

On the other hand, the Theory now proposed explains this operation, of forming those conical mountains of Sicily, and hollowing out its valleys, by known causes, and by employing powers the most necessary, the most constant, and the most general, that act upon the surface of the earth.

But, besides explaining this change of land and water by an unknown cause, our author has here employed, for the removing of this ma.s.s of solid rock, powers which appear to me no ways adequate to the end proposed. The running of water upon the soft mud left by a river, given here as an example, corresponds indeed in some respects with the form of valleys; for, water acts upon the same principle, whether it makes a channel through the subtile sediment of a river, or through the travelled materials of a valley. But it is not here that there is any difficulty in conceiving the rivers of Sicily to have shaped the mountains and the valleys; it is in removing the ma.s.ses of solid rock, which covered the whole surface of this land in successive strata, that any doubt could occur in ascribing the actual appearances of things to the natural operations of the earth; but it is here particularly that the retreat of the sea, in whatever manner supposed to be done, is altogether incompetent for the purpose which is now considered. I flatter myself, that when the Chevalier de Dolomieu, who has employed his uncommon talents in examining and elucidating the effects of fire in the bowels of those burning mountains, shall consider and examine the effects of time upon the surface of the earth, he will be ready to adopt my opinion, that there is no occasion to have recourse to any unknown cause, in explaining appearances which are every where to be found, although not always attended with such remarkable circ.u.mstances as those with which his labours have enriched natural history.

It may be proper to give a view of the operations of nature upon the Apennines. It is from an account of a journey into the province of Abruzzo, by Sir William Hamilton. Phil. Trans. 1786.

The road follows the windings of the Garigliano, which is here a beautiful clear trout stream, with a great variety of cascades and water-falls, particularly a double one at Isola, near which place CICERO had a villa; and there are still some remains of it, though converted into a chapel. The valley is extensive, and rich with fruit trees, corn, vines, and olives. Large tracts of land are here and there covered with woods of oak and chestnut, all timber trees of the largest size. The mountains nearest the valley rise gently, and are adorned with either modern castles towns, and villages, or the ruins of ancient ones. The next range of mountains, rising behind these, are covered with pines, larches, and such trees and shrubs as usually abound in a like situation; and above them a third range of mountains and rocks, being the most elevated part of the Apennine, rise much higher, and, being covered with eternal snow, make a beautiful contrast with the rich valley above mentioned; and the snow is at so great a distance as not to give that uncomfortable chill to the air which I have always found in the narrow valleys of the Alps and the Tyrol.

Having thus examined the alpine countries both of the Old World and the New, it remains to observe some river in a more low or level country emptying itself into a sea that does not communicate with the ocean. The Wolga will now serve for this purpose; and we shall take our facts from the observations of those men of science who were employed by their enlightened Sovereign to give the natural as well as the economical history of her dominions.

Russia may be considered as a square plain, containing about 40 degrees of longitude, and 20 of lat.i.tude, that is, between the 47 and 67 degrees. The east side is bounded by the Oural mountains, running in a straight line from north to south. The west is bounded by Poland. The south reaches to the Caspian and Black Seas, as does the north to the Polar Ocean.

The greatest part of the water which falls upon this extensive country is delivered into the Caspian by the river Wolga; and this water runs from the east and west sides, gathered in two great rivers, the Kama and the Oka. The water thus gathered from the two opposite extremities of this great kingdom meet in the middle with the Wolga, which receives its water from the north side. We thus find the water of this great plain running in all directions to its centre. Had this been the lowest place, here would have been formed a sea or lake. But this water found a lower place in the bed of the Caspian; and into this bason it has made its way, in forming to itself a channel in the great plain of the Wolga.

Our present purpose is to show that this channel, which the Wolga has cut for itself, had been once a continued ma.s.s of solid rock and horizontal strata, which in the course of time has been hollowed out to form a channel for those waters. These waters have been traversing all that plain, and have left protuberances as so many testimonies of what had before existed; for, we here find the horizontal strata cut down and worn away by the rivers.

M. Pallas gives us very good reason to believe that the Caspian Sea had formerly occupied a much greater extent than at present; there are the marks of its ancient banks; and the sh.e.l.ls peculiar to the Caspian Sea are found in the soil of that part of its ancient bottom which it has now deserted, and which forms the low saline _Steppe_. He also makes it extremely probable that the Caspian then communicated with the Euxine or Black Sea, and that the breaking through of the channel from the Euxine into the Mediterranean had occasioned the disjunction of those seas which had been before united, as the surface of the Caspian is lowered by the great evaporation from that sea surrounded with dry deserts.

However that may he, it is plain, that throughout all this great flat inland country of Russia, the solid rocks are decaying and wearing away by the operation of water, as certainly, though perhaps not so rapidly, as in the more mountainous regions of the earth.

If there is so much of the solid parts worn and washed away upon the surface of this earth, as represented in our Theory; and if the rivers have run so long in their present courses, it may perhaps be demanded, Why are not all the lakes filled up with soil; and why have not the Black and Caspian Seas become land or marshy ground, with rivers pa.s.sing through them to the ocean? Here is a question that may be considered either as being general to all the lakes upon the earth, or as particular to every lake which should thus find a proper explanation in the Theory. With regard to the last of these, the question has already been considered in this view, when the particular case of the Rhone was taken as an example; and now we are only to consider the question as general to the globe, or so far as belonging to the Theory, without particularising any one case.

It must be evident, that the objection to the Theory, here supposed to be made, is founded necessarily upon this, that the solid basis of our continent, on whose surface are found the lakes in question, is preserved without change, because, otherwise, the smallest variation in the basis may produce the most sensible effects upon the surface; and in this manner might be produced dry land where there had been a lake, or a lake where none had been before. But, as the present Theory is founded upon no such principle of stability in the basis of our land, no objection, to the wasting operations of the surface of the earth, can be formed against our Theory, from the consideration of those lakes, when the immediate cause of them should not appear.

The natural tendency of the operations of water upon the surface of this earth is to form a system of rivers every where, and to fill up occasional lakes. The system of rivers is executed by wearing and wasting away the surface of the earth; and this, it must be allowed, is perfect or complete, at least so far as consistent with another system, which would also appear to be in nature. This is a system of lakes with which the rivers are properly connected. Now, as there are more way than one by which a lake may be formed, consistent with the Theory, the particular explanation of every lake must be left to the natural history of the place, so far as this shall be found sufficient for the purpose.

There are many places which give certain appearances, from which it is concluded, by most intelligent observators, that there had formerly existed great lakes of fresh water, which had been drained by the discharge of those waters through conduits formed by some natural operation; and those naturalists seem to be disposed to attribute to some great convulsion, rather than to the slow operation of a rivulet, those changes which may be observed upon the surface of the earth. Let us now examine some of those appearances, in order to connect them with that general system of moving water which we have been representing as every where modifying the surface of the earth on which we dwell.

It is the P. Chrysologue De Gy, who gives the following description.

Journal de Physique, Avril 1787.

La princ.i.p.aute de Porrentrui l'emporte encore en ce genre sur le reste du Jura a ce qu'il paroit. On pourra en juger sur les circonstances locales que je vais rapporter. Une partie de cette princ.i.p.aute est divisee en quatre grandes vallees, d'environs quatre lieues de long, sur trois quarts-d'heure ou une heure de large, separees par autant de chaines de montagnes fort eleves et large en quelques endroits d'une lieue et demie. Les extremites de chacune de ces vallees sont plus elevees que le milieu, et on ne peut pas en sortir par ces extremites sans beaucoup monter. Mais ces vallees ont des communications entr'elles par une pente a.s.sez douce a travers ces ma.s.ses enormes de montagnes qui les separent, et qui sont coupees au niveau du milieu des vallees sur 300, 400, 500 toises de hauteur et dans toute leur largeur. On pourroit a.s.sez justement comparer ces vallees a des berceaux poses les uns a cote des autres, dont les extremites, remplies en talus, seroient plus eleves que les cotes, et dont ces cotes seroient coupes jusqu'au fond, pour laisser une pa.s.sage de l'un a l'autre. Je connois sept a huit pa.s.sages semblables a travers ces hautes montagnes, dans une quarre d'environ quatre a cinq lieues; et dont quatre aboutissent a la vallee de Mouthier-Grand-Val. Ces pa.s.sages sont evases dans le dessus, d'environ une demi-lieue par endroits; mais leurs parois, en talus, se rejoignent dans le fond ou coule un ruisseau. On a pratique des routes sur quelques-uns de ces talus, mais les roches sont quelquefois si resserrees et si escarpees, qu'on a ete oblige de construire un ca.n.a.l sur le ruisseau, pour y faire pa.s.ser la route. C'est-la que l'on voit a son aise, la nature de ces rochers primitives, leur direction, leur inclinaison, et tous leurs autres accidens qui demanderaient chacun une dissertation particuliere trop longue pour le moment, et il faut les avoir vues pour se faire une juste idee des sentimens de grandeur, de surprise, et d'admiration qu'elles inspirent, et que l'on ne peut pas exprimer par des paroles. Cependant, les sources de ruisseaux, ou si l'on veut des rivieres qui traversent ces montagnes, sont beaucoup plus ba.s.ses que les sommites des montagnes elles-memes, ces sources ne font donc pas la cause de ces effets merveilleux. Il a fallu un agent plus puissant pour creuser ces abimes.

M. de la Metherie has taken a very enlightened view of the country of France; and has given us a plan of the different ridges of mountains that may be traced in that kingdom, (Journal de Physique, Janvier 1787).

Now there is a double purpose in natural history to which such a plan as this may be applied; viz. first, to trace the nature of the solid parts, on which the soil for vegetation rests; and, secondly, to trace the nature of the soil or cultivated surface of the earth, on which depends the growth of plants.

With regard to the first, we may see here the granite raising up the strata, and bringing them to the light, where they appear on each side of those centrical ridges. What M. de la Metherie calls _Monts Secondaires_, I would call the proper strata of the globe, whether primary or secondary; and the _Monts Granit_, I would consider as mineral ma.s.ses, which truly, or in a certain sense, are secondary, as having been made to invade, in a fluid state, the strata from below, when they were under water; and which ma.s.ses had served to raise the country above the level of the ocean.

But this is not the subject here immediately under consideration; we are now tracing the operations of rivers upon the surface of the earth, in order to see in the present state of things a former state, and to explain the apparent irregularity of the surface and confusion of the various mineral bodies, by finding order in the works of nature; or a general system of the globe, in which the preservation of the habitable world is consulted.

For this last purpose also the mineral map of M. de la Metherie is valuable. It gives us a plan of the valleys of the great rivers, and their various branches, which, however infinitely ramified, may be considered as forming each one great valley watered, or rather drained, by its proper river. But the view I would now wish to take of those valleys, is that of habitable and fertile countries formed by the attrition of those rivers; and to perceive the operation of water wearing down the softer and less solid parts, while the more hard and solid rocks of the ridges, as well as scattered mountains, had resisted and preserved a higher station.

In this map, for example, let us suppose the first and second ridge of our author's plan to be joined at the mouth of the Loire, and retain the water of that river, as high as the summit of its surrounding ridges; this great valley of the Loire, which at present is so fine and fertile a country, would become a lake; in like manner as the proper valley of the Rhone, above St Maurice, would be drowned by shutting up that gap of the mountains through which the Rhone pa.s.ses in order to enter the plain of Geneva.

This is the view that P. Chrysologue takes of those small valleys formed between the ridges of the Jura. But this is not perhaps the just view of the subject; for though by closing the gap by which the Loire or Rhone, pa.s.ses through the inclosing ridge, the present country above would certainly be overflowed by the acc.u.mulated waters, yet it is more natural to suppose, that the great gap of the Loire, or the Rhone, had been formed gradually, in proportion as the inclosed country had been worn down and transported to the sea. We have but to consider, that the attrition of those transported materials must have been as necessary for the hollowing out of those gaps in the solid rock of the obstructing mountains, as the opening of those gaps may have been for the transporting of those materials to the sea. But it is perhaps impossible, from the present appearance of things, to see what revolutions may have happened to this country in the course of its degradation; what lakes may have been formed; what mountains of softer materials may have been levelled; and what basons of water filled up and obliterated.

This general view of the valley of the Loire, and all its branches, is perhaps too extensive to be admitted in this reasoning from effect to cause; we must approximate it by an intermediate step, which will easily be acknowledged as entering within the rule. It is in Forrez, near the head of the Loire. There we find the plain of Mont Brison, 40,000 toises or 22 miles long and half as wide, surrounded by a ridge of granite mountains on every side. Here the river, which is a small branch of the Loire, enters at the upper end of the plain (as M. de Bournon has described)[29] Par une gorge tres etroite et tortueuse, and goes out in like manner at the under End.

[Footnote 29: Journal de Physique, Mai 1787.]

Those French philosophers, who have seen this plain, have little doubts of this having been a lake, that is to say, they easily admit of the original continuity of those ridges of mountains in which the gaps are now found, through which the river pa.s.ses. But upon those principles it must be evident, that the river has hollowed out that plain, at the same time that it had formed the gaps in those ridges of the granite mountains. The only solid part, or original stratum, which M. de Bournon has described as having seen in this plain, is a decomposing _gres_ or sandstone; but there is reason to suppose, that there had been both calcareous and argillaceous or marly strata filling the hollow of that s.p.a.ce which is inclosed by the granite mountains; consequently, no difficulty in conceiving that the river, which must wear away a pa.s.sage through those mountains, should also hollow out the softer materials within, and thus form the plain, or rather a succession of plains, in proportion as the level of the water had been lowered with the wearing mountains.

If we are allowed to make this step, which I think can hardly be refused, we may proceed to enlarge our view, by comprehending, first, the Vallais of the Rhone, secondly, the countries of the Seine and Rhone, above the mountains through which those two rivers in conjunction have broke, below Lyons; and, lastly, that country of the Rhone and Durance which is almost inclosed by the surrounding mountains, meeting at the mouth of the Rhone. But this reasoning will equally apply to the countries of the Garonne, the Loire, and the Seine.

One observation more may now be made with regard to the courses of great rivers, and the fertile countries which they form in depositing the travelled soil; it is this. That though those rivers have hollowed out their beds and raised their banks; though they are constantly operating in forming fertile soil in one place and destroying it in another; and though, in many particular situations, the fertile countries, formed at the mouths of those rivers, are visibly upon the increase, yet the general progress of those operations is so slow, that human history does not serve to give us information almost of any former state of things.

The Nile will serve as an example of this fact.

The river Nile, which rises in the heights of Ethiopia, runs an amazing tract through desert countries, and discharges its waters near the bottom of the Mediterranean sea, fertilizes a long valley among barren countries with which it is surrounded, and thus lays the foundation of a kingdom, which, from its situation and the number of people it can maintain and easily bring together for any manner of action, is perhaps the strongest that can well be imagined. Accordingly, it has been of old a great kingdom, that is to say, a powerful state within itself; and has left monuments of this power, which have long been the admiration of the world. The most ancient Grecian Histories mention these monuments as being no better known, with regard to their dates and authors, than they are at this day.

The conclusion here meant to be drawn is this, that, in a period of time much more ancient than the most ancient periods in human history, Egypt had been a country formed and watered by the Nile in like manner as it is at present; that though continual changes are making in this as well as in every other river, yet, on the whole, no sensible alteration can be discerned within the compa.s.s of human experience, consequently, it is only by considering, in a scientific manner, the nature of things, and making allowances for operations which have taken place in time past, that any competent judgment can be formed of the present shape and condition of countries, or of any particular place upon the surface of this earth, so far as regards its date, its causes, or its future state.

Nothing, almost, but the kingdom of Egypt would have formed those stupendous monuments of art and labour; and nothing but the present state of Egypt, fertilised by the Nile, could have formed that powerful kingdom which might execute those works.

Thus there is a system of mountains and valleys, of hills and plains, of rivulets and rivers, all of which are so perfectly connected, and so admirably proportioned, in their forms and quant.i.ties, like the arteries and veins of the animal body, that it would be absurd to suppose any thing but wisdom could have designed this system of the earth, in delivering water to run from the higher ground; or that any thing could have formed this beautiful disposition of things but the operation of the most steady causes; operations which, in the unlimited succession of time, has brought to our view scenes which seem to us to have been always, or to have been in the original construction of this earth.

To suppose the currents of the ocean to have formed that system of hill and dale, of branching rivers and rivulets, divided almost _ad infinitum_, which a.s.semble together the water poured at large upon the surface of the earth, in order to nourish a great diversity of animals calculated for that moving element, and which carry back to the sea the superfluity of water, would be to suppose a systematic order in the currents of the ocean, an order which, with as much reason, we might look for, in the wind. The diversity of heights upon the surface of the earth, and of hardness and solidity in the ma.s.ses of which the land is formed, is doubtless governed by causes proper to the mineral kingdom, and independent either of the atmosphere or sea; but the form and structure by which the surface of the earth is fitted peculiarly to the purpose of this living world, in giving a fertility which sustains both plants and animals, is only caused by those powers which work upon the surface of the earth,--those powers, the operation of which men in general see with indifference every day, sometimes with horror or apprehension.

The system of sustaining plants and animals upon a surface where fertility abounds, and where even the desert has its proper use, is to be perceived from the summit of the mountain to the sh.o.r.e within the region of the sea; and although we have princ.i.p.ally taken the Alps, or alpine situations, for particular examples, in ill.u.s.trating this operation of the waters upon the surface of the earth, it is because the effects are here more obvious to every inquirer, and not because there is here to be acknowledged any other principle than that which is to be found on all the surface of the earth, a principle of generation in one sense, and of destruction in another.

We may also find in this particular, a certain degree of confirmation to another part of the same theory; a part which does not come so immediately within our view, and concerning which so many contradictory hypotheses have been formed. Naturalists have supposed a certain original construction of mountains, which const.i.tution of things, however, they never have explained; they have also distinguished those which have evidently been formed in another manner, that is to say, those the materials of which had been collected in the ocean. Now, here are two things perfectly different; on the one hand original mountains formed by nature, but we know not how, endued with solidity, but not differing in this respect from those of a posterior formation; on the other hand, secondary mountains, formed by the collection of materials in the sea, therefore, not having solidity as a quality inherent in their const.i.tution, but only occasional or accidental in their nature.

If, therefore, it be the natural const.i.tution of things upon the surface of this earth to indurate and become solid, however originally formed loose and incoherent, we should thus find an explanation of the consolidation of those ma.s.ses which had been lately formed of the loose materials of the ocean; if, on the contrary, we find those pretended primitive mountains, those bodies which are endued with hardness and solidity, wasting by the hand of time, and thus wearing in the operations natural to the surface of the earth, Where shall we find the consolidating operations, those by which beds of sh.e.l.ls have been transformed into perfect marble, and siliceous bodies into solid flint?

or how reconcile those opposite intentions in the same cause?

Nothing can be more absurd than to suppose a collection of sh.e.l.ls and corals, ama.s.sed about the primitive mountains of the earth, to become mountains equally solid with the others, upon the removal of the sea; it would be inconsistent with every principle of sound reasoning to suppose those ma.s.ses of loose materials to oppose equal resistance to the wasting and destroying operations of the surface of the earth, as do those pretended primitive ma.s.ses, which might be supposed endued with natural hardness and solidity; yet, consult the matter of fact, and it does not appear that there is any difference to be perceived. There are lofty mountains to be found both of the one kind and the other; both those different ma.s.ses yield to the wasting operations of the surface; and they are both carried away with the descending waters of the earth.

It is not here meant to affirm, that a ma.s.s of marble, which is a calcareous substance, opposes equal resistance, whether to the operations of dissolution or attrition, as a ma.s.s composed of granite or of quartz; it is only here maintained that there are in the Alps lofty mountains of marble, as there are in other places lower ma.s.ses of granite and its accompanying schistus. But that which is particularly to be attended to here is this: In all countries of the earth, whether of primitive ma.s.ses or those of secondary formation, whether uniform and h.o.m.ogeneous, or compound and mixed of those two different kinds of bodies, the system is always the same, of hills and valleys, lakes and rivers, ravines and streams: no man can say, by looking into the most perfect map, what is primary or what secondary in the const.i.tution of the globe. It is the same system of larger rivers branching into lesser and lesser in a continued series, of smaller rivers in like manner branching into rivulets, and of rivulets terminating at last into springs or temporary streams. The principle is universal; and, having learned the natural history of one river, we know the const.i.tution of every other upon the face of the earth.

Thus all the surface of this earth is formed according to a regular system of heights and hollows, hills and valleys, rivulets and rivers, and these rivers return the waters of the atmosphere into the general ma.s.s, in like manner as the blood, returning to the heart, is conducted in the veins. But as the solid land, formed at the bottom of the sea or in the bowels of the earth, could not be there constructed according to that system of things which we find so widely pursued upon the surface of the globe, it must be by wasting the solid parts of the land that this system of the surface has been formed, in like manner as it is by the operations of the sea that the shape of the land is determined, upon the sh.o.r.e.

Thus it has been shown, that the general tendency of the operations natural to the surface of the globe is to wear the surface of the earth, and waste the land; consequently that, however long the continents of this earth may be supposed to last, they are on the whole in a constant state of diminution and decay; and, in the progress of time, will naturally disappear. Hence confirmation is added to that mineral system of the earth, by which the present land is supposed to have acquired solidity and hardness; and according to which future land is supposed to be preparing from the materials of the sea and former continents; which land will be brought to light in time, to supply the place of that which necessarily wastes, in serving plants and animals. But what is here more particularly to the purpose is this; that we find an explanation of that various shape and conformation which is to be observed upon the surface of this earth, as being the effect of causes which are constant and unremitting in their operation, which are widely adapted to the end or absolutely necessary in the system of this world, and which, in the indefinite course of time, become unlimited in their effect, or powerful in any conceivable degree.

It is not sufficient for establis.h.i.+ng the present theory, to refute that most unscientific hypothesis, adopted by some eminent philosophers, of mountains and valleys being the effect of currents in the ocean; it is necessary to see what is their proper cause, and to show that by no other cause known could the general effect, which is of such importance in the system of this world, be actually produced. It is for this reason that we have endeavoured to show that there is a general, an universal system of river and valley, which renders the surface of this earth a sort of organized body destined to a purpose which it perfectly fulfils.

But to see the full force of this argument, taken from that order of things which is perceived in that system of valley and river all over the earth, let us examine, first, what would be the effect, in the const.i.tution of this world, of bodies of land formed upon no such system; and, secondly, what would be the effect of the natural const.i.tution of this world and meteorological operations of the atmosphere, if continued for a sufficient length of time, upon a ma.s.s of land without any systematic form.

For this purpose we shall take for example a portion of this earth, which is the best known to us, that is the south-western part of Europe, in order to compare its present state, which so perfectly fulfils the purpose of this world, with that in which no order of valley and of rivers should be fund.

Let us begin at the summit, which is the Mont-Blanc. At present the water, falling from the heavens upon this continent, is gathered into a system of rivers which run through valleys, and is delivered at last into the Adriatic, the Mediterranean, the Atlantic, and the German Seas; all the rest of this continent, except some lakes and marshes, is dry land, properly calculated, for the sustenance of a variety of plants and animals, and so fulfils the purpose of a habitable earth. Now, destroy that system of river and valley, and the whole would become a mixture of lakes and marshes, except the summits of a few barren rocks and mountains. No regular channels for conveying the super-abundant water being made, every thing must be deluged, and nothing but a system of aquatic plants and animals appear. A continent of this sort is not found upon the globe; and such a const.i.tution of things, in general, would not answer the purpose of the habitable world which we possess. It is therefore necessary to modify the surface of such a continent of land, as had been formed in the sea, and produced, by whatever means, into the atmosphere for the purpose of maintaining that variety of plants and animals which we behold; and now we are to examine how far the proper means for that modification is to be found necessarily in the const.i.tution of this world.

If we consider our continent as composed of such materials as may decay by the influence of the atmosphere, and be moved by water descending from the higher to the lower ground, as is actually the case with the land of our globe, then the water would gradually form channels in which it would run from place to place; and those channels, continually uniting as they proceed to the sea or sh.o.r.e, would form a system of rivers and their branchings. But this system of moving water must gradually produce valleys, by carrying away stones and earthy matter in their floods; and those valleys would be changing according to the softness, and hardness, destructability or indestructability of the solid parts below. Still however the system of valley and river would be preserved; and to this would be added the system of mountains, and valleys, of hills and plains, to the formation of which the unequal wearing down of the solids must in a great measure contribute.

Here therefore it is evident, _first_, that the great system upon the surface of this earth, is that of valleys and rivers; _secondly_, that no such system could arise from the operations of the sea when covering the nascent land; _thirdly_, that this system is accomplished by the same means which, are employed for procuring soil from the decaying rocks and strata; and, _lastly_, that however this system shall be interrupted and occasionally destroyed, it would necessarily be again formed in time, while the earth continued above the level of the sea.

Whatever changes take place from the operation of internal causes, the habitable earth, in general, is always preserved with the vigour of youth, and the perfection of the most mature age. We cannot see man cultivate the field, without perceiving that system of dry land provided by nature in forming valleys and rivers; we cannot study the rocks and solid strata of the earth, those bulwarks of the field and sh.o.r.e, without acknowledging the provident design of nature in giving as much permanency to our continent, as is consistent with sufficient fertility; and we cannot contemplate the necessary waste of a present continent, without perceiving the means for laying the foundation of another. But the evidence of those truths is not open to a vulgar view; _media_ are required, or much reasoning; and between the first link and the last, in this chain, what a distance, from the wasting of hard bodies upon the surface of the earth, to the formation of a solid rock at the bottom of the sea.