Part 3

We even find the first productions of these mollusca and zoophytes appearing in small numbers, and scattered at greater or less distances, in the last strata of these primitive formations, or in that portion of the crust of the globe to which geologists have given the name of Transition rocks. Here and there we meet with beds containing shells, interposed between certain granites of later formation than the others, between schists of various kinds, and between some newer beds of granular marbles. Life, which was in the end to obtain entire possession of the globe, seems, in these primordial times, to have struggled with the inert nature which formerly predominated; and it was not until a considerable time after, that it obtained the ascendancy over it, and acquired for itself the exclusive right of continuing and elevating the solid envelope of the Earth.

Hence, it is impossible to deny, that the masses which now constitute our highest mountains, have been originally in a liquid state; and that they have for a long time been covered by waters in which no living beings existed. Thus, it has not been only since the appearance of life that changes have been operated in the nature of the matters which have been deposited; for the masses formed previous to that event, have varied, as well as those which have been formed since. They have also experienced violent changes in their position, and a part of these changes must have taken place at the period when these masses existed by themselves, and were not covered over by the shelly masses. The proof of this lies in the overturnings, the disruptions, and the fissures, which are observable in their strata, as well as in those of more recent formations, and which are in the ancient strata even in greater number and better defined.

But these primitive masses have also undergone other revolutions since the formation of the secondary strata, and have, perhaps, given rise to, or at least have partaken of, some of those changes which these strata themselves have experienced. There are actually considerable portions of the primitive formations uncovered, although placed in lower situations than many of the secondary formations; and we cannot conceive how it should have so happened, unless the primitive strata in those places had forced themselves into view, after the secondary strata had been formed. In certain countries, we find numerous large blocks of primitive substances scattered over the surface of secondary formations, and separated by deep valleys, or even by arms of the sea, from the peaks or ridges from which they must have been derived. We must necessarily conclude, therefore, either that these blocks have been ejected by eruptions, or that the valleys (which must have stopped their course) did not exist at the time of their being transported; or, lastly, that the motions of the waters by which they were transported, exceeded in violence any thing that we can imagine at the present day[6].

Here, therefore, we have a collection of facts, a series of epochs, anterior to the present time, of which the successive steps may be perfectly ascertained, although the duration of their intervals cannot be defined with precision. They are so many fixed points, which serve to regulate and direct our inquiries respecting this ancient chronology.

_Examination of the Causes which act at present on the surface of the Globe._

Let us now examine those changes which are taking place at the present day upon the globe, investigating the causes which still act in its surface, and endeavouring to determine the possible extent of their effects. This portion of the history of the Earth is so much the more important, that it has long been considered possible to explain the more ancient revolutions on its surface by means of these still existing causes; in the same manner as it is found easy to explain past events in political history, by an acquaintance with the passions and intrigues of the present day. But we shall presently see, that unfortunately the case is different in physical history:--the thread of operations is here broken; the march of Nature is changed; and none of the agents which she now employs, would have been sufficient for the production of her ancient works.

There still exist, however, four causes in full activity, which contribute to alter the surface of our continents. These are, rains and thaws, which waste down the steep mountains, and precipitate the fragments to their bottoms; running waters, which carry off these fragments, and deposit them in places where their current is abated; the sea, which undermines the foundations of elevated coasts, forming steep cliffs, and which throws up great banks of sand upon the low coasts; and, lastly, volcanoes, which pierce through the solid strata from below, elevate these strata, or spread over the surface vast quantities of ejected matter[7].

_Of Slips, or Falling down of the Materials of Mountains._

In every place where the broken strata present their edges on abrupt surfaces, there fall down to their base, every spring, and even after every storm, fragments of their materials, which are rounded by rolling upon each other. These collected heaps gradually assume an inclination determined by the laws of cohesion, and thus form, at the bottom of the cliff, taluses, of greater or less elevation, according as the fragments which have fallen are more or less abundant. These taluses constitute the sides of the valleys in all elevated, mountainous regions, and are covered with a rich vegetation, whenever the fragments from the upper parts begin to fall less abundantly; but their want of solidity subjects themselves also to slips, when they are undermined by rivulets. On these occasions, towns, and rich and populous districts, are sometimes buried under the ruins of a mountain; the courses of rivers are interrupted, and lakes are formed in places which were before the abodes of fertility and cheerfulness. Fortunately these great slips happen but seldom, and the principal use of those hills of debris, is to furnish materials for the ravages of torrents.

_Alluvial Formations[8]._

The rains which fall, the vapours which are condensed, and the snows which are melted, upon the ridges and summits of mountains, descend, by an infinite number of rills, along their slopes, carrying with them some portions of the materials of which these slopes are composed, and tracing slight furrows by their passage. These rills soon unite in the deeper gutters with which the surface is marked, run off by the deep valleys which intersect their bottom, and thus form streams and rivers, which carry back to the sea the waters it had formerly supplied to the atmosphere. On the melting of the snows, or when a storm takes place, these mountain torrents become suddenly swollen, and rush down the declivities with a velocity proportioned to their steepness. They dash violently against the bases of those taluses of fallen fragments which cover the sides of all the high valleys, carrying off the already rounded fragments of which they are composed, and which thus become smoothed, and still farther polished, by attrition. But in proportion as they reach the more level valleys, where their violence is diminished, or when they arrive at more expanded basins, where their waters are permitted to spread, they throw out upon their banks the largest of those stones which they had rolled down. The smaller fragments are deposited still lower; and nothing reaches the great canal of the river excepting the minutest particles, or the most impalpable mud. It often happens, also, that before these streams unite to form great rivers, they have to pass through large and deep lakes, in which their mud is deposited, and from which their waters come forth limpid.

The lower rivers, and all the streams which descend from the less elevated mountains and hills, also produce effects, upon the districts through which they flow, more or less analogous to those of the torrents from the higher mountains. When these rivers are swollen by great rains, they attack the base of the earthy or sandy hills which they meet with in their course, and carry their fragments to be deposited upon the lower grounds, and which are thus, in some degree, raised by each succeeding inundation. Finally, when the rivers reach great lakes or the sea, and when that rapidity, which carried off and kept in suspension the particles of mud comes to cease entirely, these particles are deposited at the sides of their mouths, where they form low grounds, by which the shores are prolonged. And if these shores are such, that the sea also throws up sand upon them, and thus contributes to their increase; there are created, as it were, provinces, and even entire kingdoms, which usually become the most fertile, and speedily the richest, in the world, if their rulers permit human industry to exert itself in peace.

_Formation of Downs._[9]

The effects which the sea produces, without the co-operation of rivers, are much less beneficial. When the coast is low, and the bottom sandy, the waves push the sand toward the shore, where, at every reflux of the tide, it becomes partially dried; and the wind, which almost always blows from the sea, drifts it upon the beach. Thus are formed those hillocks of sand, named Downs, which, if the industry of man does not fix them by suitable plants, move slowly, but invariably, toward the interior of the country, and overwhelm fields and dwellings, because the same wind that raises the sand of the beach upon the down, throws that of its summit in the opposite direction from the sea. When the nature of the sand, and that of the water which is raised with it, are such as to form a durable cement, the shells and bones, thrown upon the beach, become incrusted with it. Pieces of wood, trunks of trees, and plants growing near the sea, are enveloped in these aggregates; and thus are produced what might be denominated _indurated downs_, such as we see upon the coasts of New Holland, and of which a precise idea may be formed from the description given of them by Peron[10].

_Formation of Cliffs or Steep Shores._

On the other hand, when the coast is high, the sea, which is thus prevented from throwing up any thing, exercises a destructive action upon it. Its waves, by sapping the foundation, cause the superincumbent portion of the face of the cliff, thus deprived of support, to be incessantly falling down in fragments. These fragments are tumbled about by the billows, until the softer and more divided parts disappear. The harder portions, from being rolled in contrary directions, assume the form of boulders and pebbles; and these, at length, accumulate in sufficient quantity to form a rampart, by which the bottom of the cliff is protected against farther depredations.

* * * * *

Such is the action of water upon the solid land; and we see, that it consists almost entirely in reducing it to lower levels, but not indefinitely. The fragments of the great mountain ridges are carried down into the valleys; their finer particles, together with those of the lower hills and plains, are borne to the sea; alluvial depositions extend the coasts at the expence of the high grounds. These are limited effects, to which vegetation in general puts a stop, and which, besides, presuppose the existence of mountains, valleys, and plains, in short, all the inequalities of the globe; and which, therefore, cannot have given rise to these inequalities. The formation of downs is a phenomenon still more limited, both in regard to height and horizontal extent; and has no relation whatever to that of those enormous masses into the origin of which it is the object of geology to inquire.[11]

_Depositions formed in Water._

Although we cannot obtain a precise knowledge of the action exerted by water within its own bosom, it is yet possible to determine its limits to a certain degree.

Lakes, pools, marshes, and sea-ports, into which rivulets discharge their waters, more especially when these descend from near and steep hills, deposit large quantities of mud, which would at length fill them up entirely, if care were not taken to clean them out. The sea also throws quantities of slime and sediment into harbours and creeks; into all places, in short, where its waters are more tranquil than ordinary. The currents also heap up at their meeting, or throw out at their sides, the sand which they are continually raising from the bottom of the sea, forming it into banks and shallows.

_Stalactites._

Certain waters, after dissolving calcareous substances by means of the superabundant carbonic acid with which they are impregnated, allow these substances to crystallize after the acid has evaporated; and, in this manner, form stalactites, and other concretions. There are strata, confusedly crystallized in fresh water, which are sufficiently extensive to be compared with some of those which have been deposited by the ancient sea. The famous Travertine quarries of the neighbourhood of Rome, and the rocks of the same substance, which are formed, and continually varied in figure, by the river of Teverona, are generally known. These two modes of action may be combined; the deposits accumulated by the sea may be solidified by stalactite. Thus, when springs abounding in calcareous matter, or containing some other substance in solution, happen to fall into places where these deposits are formed, we then find aggregates in which marine and fresh-water productions may be blended. Of this description are the banks in the island of Guadeloupe, which, along with human skeletons, present land and sea shells mingled together. Of the same nature also is the quarry described by Saussure, in the neighbourhood of Messina, in which the sandstone is seen forming by the consolidation of the sand thrown up by the sea.

_Lithophytes._

In the torrid zone, where lithophytes of many species abound, and are propagated with great rapidity, their strong trunks are interwoven and accumulated so as to form rocks and reefs; and rising even to the surface of the water, shut up the entrance of harbours, and lay frightful snares for navigators. The sea, throwing up sand and mud upon the tops of these shoals, sometimes raises their surface above its own level, and forms islands, which are soon covered with a rich vegetation.

_Incrustation._

It is also possible, that, in particular places, large quantities of the animals inhabiting shells, leave their stony coverings when they die, and that these, cemented together by slime of greater or less consistence, or by other cementing substances, form extensive deposits or shell banks. But we have no evidence that the sea can now incrust those shells with a paste as compact as that of the marbles, the sandstones, or even the coarse limestone (calcaire grossier) in which we see the shells of our strata enveloped. Still less do we any where find the sea depositing those more solid and more siliceous strata which have preceded the formation of the shelly strata.

In short, all these causes united, would not change, in an appreciable degree, the level of the sea; nor raise a single stratum above its surface; and still less would they produce the smallest hillock upon the surface of the earth.

It has been asserted that the sea has undergone a general diminution of level; and proofs of this are said to have been discovered in some parts of the shores of the Baltic.[12] But whatever may be the causes of these appearances, we are certain that they are not general in their operation; and that, in the greater number of harbours, where any alteration of the level would be a matter of so much interest, and where fixed and ancient works afford so many means of measuring its variations, the mean level of the sea is constant. There has, therefore, never been a universal lowering, nor a universal encroachment, of the waters of the ocean. In some places, indeed, such as Scotland, and various parts of the Mediterranean, evidence has been thought to have been found, that the sea has risen, and that it now covers shores which were formerly above its level[13].

_Volcanoes._

The action of volcanoes is still more limited, and more local, than any of those which have yet been mentioned. Although we have no precise idea of the means by which nature keeps up these violent fires at such great depths, we can judge decidedly, by their effects, of the changes which they may have produced at the surface of the globe. After a volcano has announced itself, by some shocks of an earthquake, it forms for itself an opening. Stones and ashes are thrown to a great distance, and lava is vomited forth. The more fluid part of the lava flows in long streams, while the less fluid portion stops at the edges of the opening, raises its margins all round, and forms a cone, terminated by a crater. Thus volcanoes accumulate upon the surface matters which were previously buried in the bowels of the earth, after modifying their nature, and raise themselves into mountains. By these means, they have formerly covered some parts of our continent, and have also suddenly produced islands in the middle of the sea. But these mountains and islands have always been composed of lava, and all their materials have undergone the action of fire: they are disposed as matters should be, which have flowed from an elevated point. Volcanoes, therefore, neither raise nor overturn the strata through which their apertures pass; and if some causes acting from those depths have contributed, in certain cases, to raise up large mountains, they cannot have been volcanic agents of the same nature as those which exist at the present day.

* * * * *

Thus, we repeat, it is in vain that we search, among the powers which now act at the surface of the earth, for causes sufficient to produce the revolutions and catastrophes, the traces of which are exhibited by its crust: And if we have recourse to the constant external forces with which we are as yet acquainted, we shall have no greater success.

_Constant Astronomical Causes._

The pole of the earth moves in a circle around the pole of the ecliptic, and its axis is more or less inclined to the plane of the ecliptic; but these two motions, the causes of which are now ascertained, are much too limited for the production of effects like those whose magnitude we have just been stating. At any rate, their excessive slowness would render them altogether inadequate to account for catastrophes which, as we have shewn, must have been sudden.

The same reasoning applies to all other slow motions which have been conceived as causes of the revolutions in question, chosen doubtless in the hope that their existence could not be denied, because it might always be easy to hold out that their very slowness rendered them imperceptible. But whether they be true or not is of little importance, for they explain nothing, as no cause acting slowly could have produced sudden effects.

Admitting that there has been a gradual diminution of the waters; that the sea has transported solid matters in all directions; that the temperature of the globe is either diminishing or increasing;--none of these causes could have overturned our strata; enveloped in ice large animals, with their flesh and skin; laid dry marine testacea, the shells of which are, at the present day, as well preserved as if they had been drawn up alive from the sea; and, lastly, destroyed numerous species, and even entire genera.

These considerations have struck most naturalists; and among those who have endeavoured to explain the present state of the globe, hardly any one has attributed it entirely to the agency of slow causes, still less to causes operating under our eyes. The necessity to which they are thus reduced, of seeking for causes different from those which we see acting at the present day, is the very circumstance that has forced them to make so many extraordinary suppositions, and to lose themselves in so many erroneous and contradictory speculations, that the very name of their science, as I have elsewhere remarked, has long been a subject of ridicule to prejudiced persons, who have only looked to the systems which it has been the means of hatching, and have forgotten the extensive and important series of authentic facts which it has brought to light[14].

_Older Systems of Geologists._

During a long time, two events or epochs only, the Creation and the Deluge, were admitted as comprehending the changes which have been operated upon the globe; and all the efforts of geologists were directed to account for the present existing state of things, by imagining a certain original state, afterwards modified by the deluge, of which also, as to its causes, its operations, and its effects, each entertained his own theory.

Thus, according to one[15], the earth was at first invested with an uniform light crust, which covered the abyss of the sea; and which being broken up for the production of the deluge, formed the mountains by its fragments. According to another[16], the deluge was occasioned by a momentary suspension of cohesion among the particles of mineral bodies; the whole mass of the globe was dissolved, and the paste thus formed became penetrated with shells. According to a third[17], God raised up the mountains for the purpose of allowing the waters, which had produced the deluge, to run off; and selected those places in which there was the greatest quantity of rocks, without which the mountains could not have supported themselves. A fourth[18] created the earth from the atmosphere of one comet, and deluged it by the tail of another: The heat which it retained from its origin, was what, in his opinion, excited the whole of the living beings upon it to sin; for which they were all drowned, excepting the fishes, whose passions were apparently less vehement.

It is evident, that, even while confined within the limits prescribed by the Book of Genesis, naturalists might still have a pretty wide range: they soon found themselves, however, in too narrow bounds; and when they had succeeded in converting the six days of creation into so many indefinite periods, the lapse of ages no longer forming an obstacle to their views, their systems took a flight proportioned to the periods which they could then dispose of at pleasure.

Even the great Leibnitz amused himself, like Descartes, by conceiving the earth to be an extinguished sun[19], a vitrified globe, upon which the vapours falling down again, after it had cooled, formed seas, which afterwards deposited the limestone formations.

By Demaillet the whole globe was conceived to have been covered with water for many thousands of years. He supposed this water had gradually retired; that all the land animals were originally inhabitants of the sea; that man himself commenced his career as a fish; and he asserts, that it is not uncommon, even now, to meet with fishes in the ocean, which are still only half converted into men, but whose descendants will in time become perfect human beings[20].

The system of Buffon is merely an extension of that of Leibnitz, with the addition only of a comet, which, by a violent blow, struck off from the sun the liquefied mass of the earth, together with those of all the other planets at the same instant. From this supposition, he was enabled to assume positive dates, as, from the present temperature of the earth, it could be calculated how long it had taken to cool down so far; and, as all the other planets had come from the sun at the same time, it could also be calculated how many ages are still required for cooling the greater ones, and to what degree the smaller are already frozen[21].

_More recent Systems._