Theory of the Earth Volume Ii Part 8

CHAP. VII.

_The Same Subject continued, in giving a View of the Operations of Air and Water upon the Surface of the Land._

We have but to enlarge our thoughts with regard to things past by attending to what we see at present, and we shall understand many things which to a more contracted view appear to be in nature insulated or without a proper cause; such are those great blocks of granite so foreign to the place on which they stand, and so large as to seem to have been transported by some power unnatural to the place from whence they came. We have but to consider the surface of this earth as having been upon a higher level; as having been every where the beds of rivers, which had moved the matter of strata and fragments of rocks, now no more existing; and as thus disposed upon different planes, which are, like the haughs of rivers, changing in a continual succession, but changing upon a scale too slow to be perceived. M. de Luc has given a picture which is very proper to a.s.sist our imagination in contemplating a more ancient state of this earth, although in this he has a very different end in view, and means to show that the world, which we inhabit at present, is of a recent date. It is in the 32d letter of his Histoire de la Terre, which I beg leave here to transcribe.

Des montagnes ba.s.ses (comme le _Jura_, qui est bas comparativement aux Alpes) sont bientot fixees par ce moyen. Il ne se fait presque qu'un seul _talus_ depuis leur sommet jusques dans les ba.s.ses vallees, ou sur la plaine. Aussi l'etat de ces montagnes est-il deja presqu'entierement _fixe_: on y voit tres peu de rochers nuds qui s'eboulent, excepte, aupres des _rivieres_. C'est dans ces lieux-la que l'ouvrage tarde le plus a se finir. Le bas des _talus_ est mine par l'eau; leur surface s'eboule donc, pour ainsi dire, sans cesse, et laisse a decouvert les rochers des sommets, qui par la continuent aussi a _s'ebouler_. Mais les vallees s'elargissent enfin; et les _talus_ s'eloignant ainsi des _rivieres_, commencent a eprouver les influences du repos.

Here nothing can be more positively described than the natural destruction of those mountains by the operation of the rivers which run between them; and this is from the authority of matter of fact, which, on all occasions, this author faithfully describes. At the same time, we are desired to believe, upon no better authority than the imagination of a person hurried on by system, that those mountains are absolutely to come to rest. I am aware of the danger to which a spirit of systematising leads; and I wish for nothing more than to have my Theory strictly examined, in comparing it with nature.

Our author thus proceeds: La vue seule de la chaine du _Jura_ nous apprend donc ce que deviendroit enfin toutes les montagnes. Dans la plus grande partie de son etendue, il ne souffre plus aucun changement ruineux: la _vegetation_ le recouvre presque partout. Les bas sont cultives de toute sorte de maniere suivant leur exposition; les sommets sont couverts de pelouses, qui forment les paturages les plus precieux.

Cette gazonade s'etend aussi sur toutes les parties des pentes qui ne sont pas trop rapides, et le reste est couvert de bois.

J'ai parcouru fort souvent le pied de ces montagnes: leur etat est presque partout tel que je viens d'avoir l'honneur de la descrire a V.M.

J'ai sur-tout observe avec attention les lits des _torrens_ qui, en descendent pour se rendre dans les lacs de _Geneva_, de _Neufchatel_ et de _Bienne_, ainsi que dans l'Aar et dans le Rhin: et hormis ceux de ces _torrens_ qui viennent des gorges ou les terrains sont encore escarpes, ils ne roulent plus que l'ancien gravier qu'ils out apporte autrefois.

Mais il n'en est pas ainsi des _Alpes_, des _Pyrenees_, et des autres montagnes, qui, comme celles-la, sont beaucoup plus elevees, ou qui sans l'etre davantage ont ete livrees aux influences de l'air dans un desordre plus grand. Dans ce genre de montagnes il reste encore a la _vegetation_ de bien grandes conquetes a faire.

Ces montagnes ne sont pas telles que V.M. pourroit se les figurer naturellement; il faut y etre monte pour s'en former une juste idee. Ce sont des montagnes sur d'autres montagnes. De pres on ne voit que les parties inferieures; de loin tout se confond; il faut donc etre arrive sur une des premieres _terra.s.ses_ pour voir les secondes; sur celles-ci pour les troisiemes; et ainsi de suite.

La plupart de ces _terra.s.ses_ successives sont de grandes plaines, dominees par des rochers qui s'eboulent, et forment des _talus_. Si dans la succession des siecles, les _eboulemens_ de ces bandes de rochers en amphitheatre finissoient sans emporter les plaines qu'ils soutiennent, et que les _torrens_ eussent creuse leur lit pendant ce tems la a quelque distance des _talus_ tout seroit fini par cette premiere operation. Mais il y a peu de hautes montagnes ou les arrangemens soient si simples: souvent ces bandes empietent les unes sur les autres en _s'eboulant_, et alors le repos est bien differe.

Supposons que ces _terra.s.ses_ soient etroites, et que leurs murs, c'est-a-dire les rochers qui les soutiennent, soient fort eleves. Les _terra.s.ses_ alors ne suffiront pas pour recevoir les _eboulemens_ qui doivent se faire sur elles car le dessus de chacune d'elles s'etrecit de plus en plus par la destruction du rocher qui la soutient. Il pourra donc arriver que ce talus, s'etant etendu jusqu'au bord de la terra.s.se, se trouve reposer sur une base qui s'eboule encore; et meme cela arrive tres souvent; de sorte qu'a chaque retreciss.e.m.e.nt de la base, le _talus_ lui-meme s'eboule. Ainsi deux _talus_, qui etoient peut-etre deja en pleine vegetation par la lenteur des eboulemens des rochers qui les formoient, pourront etre fort recules a cet egard; le _talus_ superieur, parce que la surface fertilisee glissera en bas; et le _talus_ inferieur, parce que la sienne sera ensevelie sous de nouveaux decombres.

Les montagnes qui sont dans ce cas seront proportionnellement plus abaissees que les autres; parce que leurs _talus_ se confondant ainsi et devenant par la fort etendus demeureront longtemps a devenir solides.

Les eaux partant de fort haut, auront le tems de s'y ra.s.sembler et de devenir destructives vers le bas. Au lieu que dans les montagnes ou les terra.s.ses subsisteront encore apres que tous les rochers se seront _eboules_, les eaux etant recues par reprises, perdront beaucoup de leur rapidite. Elles se ra.s.sembleront dans les enfoncemens des pet.i.tes vallees superieures, elles s'y formeront des lits qu'elles ne rongeront presque point; et la _vegetation_ restera tranquille partout.

Let us now consider the height of the _Alps_, in general, to have been much greater than it is at present; and this is a supposition of which we have no reason to suspect the fallacy; for, the wasted summits of those mountains attest its truth. There would then have been immense valleys of ice sliding down in all directions towards the lower country, and carrying large blocks of granite to a great distance, where they would be variously deposited, and many of them remain an object of admiration to after ages, conjecturing from whence, or how they came.

Such are the great blocks of granite which now repose upon the hills of _Saleve_. M. de Saussure, who has examined them carefully, gives demonstration of the long time during which they have remained in their present place. The lime-stone bottom around being dissolved by the rain, while that which serves as the basis of those ma.s.ses stands high above the rest of the rock, in having been protected from the rain. But no natural operation of the globe can explain the transportation of those bodies of stone, except the changed state of things arising from the degradation of the mountains.

Every thing, therefore, tends to show that the surface of the earth must wear; but M. de Luc, although he allows the principles on which this reasoning is founded, labours to prove that those destructive causes will not operate in time. Now, What would be the consequence of such a system?--That the source of vegetation upon the surface of the earth would cease at last, and perfect sterility be necessarily the effect of allowing no farther degradation to the surface of the earth; for, What is to supply the matter of plants? Water, air, and light alone, will not suffice; there are necessarily required other elements which the earth alone affords. If, therefore, this world is to continue, as it has done, to form continents of calcareous strata at the bottom of the ocean, the animals which form these strata, with their _exuviae_, must be fed. But, on what can they be fed? not on water alone; the consequence of such a supposition would lead us to absurdity; nor can they be fed on any other element without the dissolution of land. According to my views of things, it is certain that those animals are ultimately fed on vegetable bodies; and it is equally certain, that plants require a soil on which they may not only fix their fibrous roots, but find their nourishment at least in part; for, that air, water, and the matter of light, also contribute, cannot be doubted. But if animals, which are to form the strata of the earth, are to be fed on plants, and these are to be nourished by the matter of this earth, the waste of vegetable matter upon the surface of the earth must be repaired; the exhausted soil must be transported from the surface of the land; and fertility must be restored by the gradual decay of solid parts, and by the successive removal of soil from stage to stage. What a reverie, therefore, is that idea, of bringing the earth to perfection by fixing the state of its vegetable surface!

The description of those natural operations, which M. de Luc has given with a view to establish the duration of the mountains, is founded upon nothing but their destruction. These beds of rivers, which, according to our author, are _hardly_ to be wasted any more, will not satisfy a philosopher, who requires to see no degree of wasting in a body which is to remain for ever, or continue without change. But, however untenable this supposition of a fixed state in the surface of this earth, the accuracy of the natural philosopher may still be observed in the absurdity of the proposition. L'etat des _montagnes_ sera _fixe_, partout ou les _rivieres_ seront arrivees au point de n'emporter pas plus de limon hors de leur enceinte, que l'air et les pluies n'y deposeront de _terre vegetable_, et voila enfin quel sera le repos, l'etat permanent de la surface de notre globe. Car alors il y aura compensation entre les destructions et les reparations simultanees, et les montagnes surement ne s'abaisseront plus.

Surely, if there is in the system of nature wisdom, we may look for compensation between the destroying and repairing operations of the globe. But why seek for this compensation in the _rest_ or immobility of things? Why suppose perfection in the want of change? The summit of the Alps was once the bottom of the sea; the existence of our land depended then upon the change of seas and continents. But has the earth already undergone so great changes, and is it not yet arrived at the period of its perfection? How can a philosopher, who is so much employed in contemplating the beauty of nature, the wisdom and goodness of Providence, allow himself to entertain such mean ideas of the system as to suppose, that, in the indefinite succession of time past, there has not been perfection in the works of nature? Every material being exists in motion, every immaterial being in action and in pa.s.sion; rest exists not any where; nor is it found in any other way, except among the parts of s.p.a.ce. Surely it is contrary to every species of philosophy, whether ancient or modern, to found a system on the inutility of repose, or place perfection in the vacuity of rest, when every thing that truly exists, exists in motion; when every real information which we have is derived from a change; and when every excess in nature is compensated, not by rest, but by alternation.

M. de Luc allows the rivers to carry matter always to the sea; but then, at a certain period, this matter carried by the floods is to be compensated to the mountains by the vegetable earth received from the air and rains. Here is a proposition which should be well considered, before it be admitted as a principle, which shall establish the perpetuity of these mountains, if it be true; or, if false, a.s.sure us of their future demolition. Let us now examine it.

If from air and rain there is produced earth which cannot afterwards be resolved by the operation of those elements, and thus again dissolved in the air and water of the land, then this author might have had some pretext, however insufficient, for alledging that it might be possible to compensate the loss of mineral substances, carried off the surface of the earth, by the production of this vegetable matter from the air and rain; but, when there is not sufficient reason to conclude that any substance, produced in vegetation, can resist the continued influences of the air and water, without being decomposed in its principles, and at last entirely dissolved in water, the cautious argument here employed by this author, for the permanency of mountains, must appear as groundless in its principle as it would be insufficient for his purpose, were it to be admitted; but this will require some discussion.

That which preserves vegetable bodies so long from dissolution in water, is what may be called the inflammable or phlogistic composition of those bodies. This composition is quickly resolved in combustion; but it is no less surely resolved by the influences of the sun and atmosphere, only in a slower manner. Therefore, to place the permanency of this earth, or any of its surface, upon a substance which in that situation necessarily decays, is to form a speculation inconsistent with the principles of natural philosophy[11].

[Footnote 11: It is from inadvertency to this fact in natural history, the consuming of vegetable substances exposed to the influences of the atmosphere, that M. de Luc, in his _Histoire de la Terre_, has pretended to determine the past duration of the German heaths as not of a very high antiquity. He has measured the increase of the vegetable soil, an increase formed by the acc.u.mulation of the decayed heath; and, from the annual increase or deposits of vegetable matter on that surface, he has formed a calculation which he then applies to every period of this turfy augmentation, not considering that there may be definitive causes which increase with this growing soil, and which, increasing at a greater rate in proportion as the soil augments, may set a period to the further augmentation of that vegetable soil. Such is fire in the burning of those parched heaths; such is the slower but constant and growing operation of the oxygenating atmosphere upon this turfy substance exposed to the air and moisture. This author has very well described the constant augmentation of this vegetable substance in the mora.s.ses of that country, as it also happens in those of our own; but there is a wide difference in those two cases of peat bog and healthy turf; the vegetable substance in the mora.s.s is under water, and therefore has its inflammable quality or combustible substance protected from the consuming operation of the vital or atmospheric air; the turfy soil, on the contrary, is exposed to this source of resolution in the other situation.]

But even supposing that the degradation of mountains were to be suspended by the pretended compensation which is formed, by the rivers carrying mineral mud into the sea, and the air and rain producing vegetable earth; in what must this operation end? In carrying into the sea, to be deposited at its bottom, all the vegetable earth produced by the air and rain. But our cosmologist, in thus procuring an eternal station to his mountains, has not told us whether this trans.m.u.tation of the air and rain be a finite operation, or one that is infinite; whether it be in other respects confident with the natural operations of the globe; and whether, to have the air and water of the globe converted into earth, would ultimately promote, or not, that perfection which he wishes to establish. Here, therefore, in allowing to this philosophy all its suppositions, it would be necessary to make another compensation, in preserving mountains at the expense of air and rain; and, the waste of air and water, which are limited, would require to be repaired.

It is not in our purpose here to treat of moral causes; but this author having endeavoured to fortify his system by observing, that the world certainly cannot be ancient, since men have not ceased as yet to quarrel and fight, (Lettre 34.) it may be proper to observe, that the absolute rest of land, like the peace among mankind, will never happen till those things are changed in their nature and const.i.tution, that is to say, until the matter of this globe shall be no more a living world, and man no more an animal that reasons from his proper knowledge, which is still imperfect. If man must learn to reason, as children learn to speak, he must reason erroneously before he reasons right; therefore, philosophers will differ in their opinions as long as there is any thing for man to learn. But this is right; for, how are false opinions to be corrected, except in being opposed by the opinions of other men? It is foolish, indeed, for men to quarrel and fight, because they differ in opinion.

Man quarrels properly, when he is angry; and anger perhaps is almost always ultimately founded upon erroneous opinion. But, in nature, there is no opinion; there is truth in every thing that is in nature; and in man alone is error. Let us, therefore, in studying nature, learn to know the truth, and not indulge erroneous notions, by endeavouring to correct, in nature, that which perhaps is only wrong in our opinion.

Having shown that every thing, which is moveable upon the surface of the land, tends to the sea, however slowly in its pace, we are now to examine, what comes of those materials deposited within the regions of the waves, still however within the reach of man, and still subservient more immediately to that soil on which plants grow, and man may dwell.

As, from the summit of the land, the natural tendency of moveable bodies is to fall into the water of the sea, so, from the borders of the land or coast, there being a declivity towards the deepest bottom of the sea, and there being currents in the waters of the ocean occasionally rendered more rapid on the sh.o.r.e, every moveable thing must tend to travel from the coast, and to proceed alone; the shelving bottom of the sea into the unfathomable deep, when they are beyond the reach of man or the possibility of returning to the sh.o.r.e.

But it is not every where upon the coast that those materials are equally delivered; neither is it every where along the sh.o.r.e that the currents of the ocean are equally perceived, or operate with equal power in moving bodies along the shelving bottom of the sea. Hence in some places deep water is found was.h.i.+ng rocky coasts, where the waste of land is only to be perceived from what is visibly wanting in the continuity of those hard and solid bodies. In other places, again, the land appears to grow and to encroach upon the s.p.a.ce which had been occupied by the sea; for here the materials of the land are so acc.u.mulated on the coast, that the bottom of the sea is filled up, and dry land is formed in the bafon of the sea, from those materials which the rivers had brought down upon the sh.o.r.e.[12]

[Footnote 12: We are not however to estimate this operation, of forming soil by the muddy waters of a river depositing sediment, in the manner that M. de Luc has endeavoured to calculate the short time elapsed in forming the marshlands of the Elbe. This philosopher, with a view to show that the present earth has not subsisted long since the time it had appeared above the surface of the sea, has given an example of the marsh of _Wisebhafen_ where the earth, wasted by inundation, was in a very little time replaced, and the soil heightened by the flowings of the Elbe, and this he marks as a leading fact or principle, in calculating the past duration of our continents, of which he says, we are not to lose sight (Tome 5, p. 136.) But here this philosopher does not seem to be aware, that he is calculating upon very false grounds, when he compares two things which are by no means alike, the natural operations of a river upon its banks, making and unmaking occasionally its haughs or level lands, that is to say, alternately making and destroying, and the artificial operations of man receiving the muddy water of a tide-way into the still water of a pond formed by his ramparts; yet, it is by this last operation that our author forms an estimate which he applies to the age of this earth, in calculating how long time might have been required for producing the marsh lands of the Elbe.

I would here ask if he can calculate what time it may have required to hollow out the bed of the Elbe from its source to the sea; and to tell how often the marsh-lands, which he now sees cultivated, had been formed and destroyed by the river before they were cultivated in their present state; or if there is any security that they shall not again be taken away by the river, and again formed in the same place. If this is the case, that the river is constantly changing the fertile lands, which it forms by its inundation, what judgement are we to form by calculating the quant.i.ty of sediment in a certain measure of its muddy water.]

Holland affords the very best example of this fact. It is a low country formed in the sea. This low land is situated in the bottom of a deep bay, or upon the coast of a shallow sea, where more materials are brought by the great rivers from the land of Germany than what the currents of the sea can carry out into the deep. Here banks of sand are gathered together by streams and tides; this sand is blown in hillocks by the wind; and those sand hills are retained by the plants which have taken root and fixed those moving sands. Behind that chain of hillocks, which line the sea sh.o.r.e, the waters of the rivers formed a lake, and the bottom of this lake had been gradually filled up or heightened by materials travelling in the rivers, and here finding rest. It grew up until it became a marsh; then man took possession of the soil; he has turned it to his own life; and, by artificial ramparts of his forming, preserves it in the present state, some parts above the level of the sea, others considerably below the ordinary rise of tides. M de Luc, who has given a very scientific view of this country in his Lettres Physiques et Morales, has there also furnished us with the following register of what had been found by sinking in that soil. It was at Amsterdam at the year 1605 in making a well.

Voici la designation des matieres qui furent trouvees en partant de la surface.

51 pieds, meles _de sable tourbeux_, de fable _des dunes pur_ et _d'argile_ ou limon.

22.---de meme _sable des dunes pur_, et _d'argile_ bleuatre.

14.---du meme _sable_ pur.

87 pieds.--Ou rien encore n'indiquoit la presence de la mer.

55.---de _sable marin_, et _de limon_, meles l'un et l'autre de _coquilles_ dans plusieurs couches.

142 pieds.--Soit la plus grande profondeur, ou s'est manifestee la _presence_ de la mer.

49.---_Argille_ dure sans melange de coquilles, soit que ce soit une couche _argilleuse continentale,_ ou les premiers depots des fleuves; ce qu'il est difficile de Determiner.

191 pieds.

13.---Sable mele de pierres; qui est enfin surement le _sol_ vierge continental.

28.---Sable pur; continental encore; car j'ai remarque partout dans la _Geest_, que c'est dans la couche superieure, a une pet.i.te profondeur que se trouvent les pierres; au-dessous le _sable_ est pur.

232 pieds.--C'est a cette profondeur, ou dans la ma.s.se de ces deux dernieres couches, que se trouva l'eau douce, et par consequent le vrai _sol continental_.

The light that we have from this pit which has been made in the soil, according to my view of the subject, is this, that here is the depth of 232 feet in travelled soil, and no solid bottom found at this distance from the surface or level of the sea. How far this depth may be from the bottom of these travelled materials is unknown; but this is certain, that all that depth, which has been sunk, had been filled up with those materials[13].

[Footnote 13: An interesting map for the use of natural history would be made by tracing the places (behind this country of loose or travelled soil) where the solid strata appear above the level of the sea. We should be thus able to form some notion of the quant.i.ty of materials which had been deposited in the water of this sea. But, though we might thus enlarge our views a little with regard to the transactions of time past, it would only be in a most imperfect manner that we would thus form a judgment; for, not knowing the quant.i.ty of sand and mud carried out by the currents from the German sea into the Atlantic, we could only thus perceive a certain minimum, which is perhaps a little portion of the whole.]

It will thus appear of what unstable materials is composed the land of that temporary country. It will also be evident, that, by removing the sand banks of this coast, the whole of this low country would be swallowed by the sea, notwithstanding every effort that the power of man could make. But it may be alledged, that those sand banks are increasing still with the alluvion of Germany, instead of being in a decreasing state. I should also incline to believe that this is truly the case; but, though we may acknowledge the growth of land upon the coast of Holland, we must deny that a stable country can be formed in the bed of the sea by such means. For, however increasing may be the sand in the German sea, and however great additions may be made of habitable country to the coast of Holland, yet, as the islands of Great Britain and Ireland are worn by attrition on the sh.o.r.es, and are wasted by being washed away into the ocean, the causes for the acc.u.mulation of sand in the German sea must cease in time, when, in this progress of things, the sand banks, on which depends the existence of Holland, must diminish, and at last be swept away, in leaving the solid coast of Germany to be again buffeted by the waves, as is at present the coasts of Ireland, France, and Spain.

This reasoning is, indeed, very far removed from that which is commonly employed for the purpose of conducting human operations, or establis.h.i.+ng the political system of a nation; it is not, however, the less interesting to man, in that it cannot direct him immediately in his worldly affairs; and it is the only way of reasoning that can be employed in order to enlighten man with a view of those operations which are not to be limited in time, and which are to be concluded as in the system of nature, a system which man contemplates with much pleasure, and studies with much profit.

Thus we have shown, that, from the top of the mountain to the sh.o.r.e of the sea, which are the two extremities of our land, every thing is in a state of change; the rock and solid strath dissolving, breaking, and decomposing, for the purpose of becoming soil; the soil travelling along the surface of the earth, in its way to the sh.o.r.e; and the sh.o.r.e wearing and wasting by the agitation of the sea, an agitation which is essential to the purposes of a living world. Without those operations, which wear and waste the coast, there would not be wind and rain; and, without those operations which wear and waste the solid land, the surface of the earth would become sterile. But showers of rain and fertile soil are necessarily required in the system of this world; consequently, the dissolution of the rocks, and solid strata of the earth, and the gradual, flow, but sure destruction of the present land, are operations necessary in the system of this world; so far from being evils, they are wisely calculated, in the system of nature, for the general good.

CHAP. VIII.

_The present Form of the Surface of the Earth explained, with a View of the Operation of Time upon our Land_.