To all these causes of upheavals and formations produced by igneous action are joined the aqueous causes, that is, the waters of the seas, lakes, and rivers; the subterranean waters, which, arriving at the surface laden with different materials—with sulfur, limestone, silica, etc.—leave there more or less considerable deposits of travertines or tuffs, of millstone rocks, etc., whose beds sometimes have a considerable thickness.
Alluvia and accretions have also furnished their share, and a fairly large share, in the formation of sedimentary terrains. We have, among other remarkable examples of them, that of the accretions of the Mississippi, of which we have already spoken. A conscientious study made by Monsieur de
Serres on the delta of this river and on the date of its formation, a study of which Le Monde has given us an account, permits us to calculate the power of fluviatile alluvia. Here is the result of these learned researches:
“We have already made clear in our Cosmogony how inaccurate are the calculations upon which reliance has been placed in order to give a high antiquity to the formation of the Mississippi delta. It results from the most positive facts that the alluvia which contribute to the accumulation of the lands of this delta, instead of effecting their deposits with excessive slowness, proceed, on the contrary, with the greatest activity. It had even been supposed that the alluvia had not advanced into the sea, during the one hundred and twenty years preceding the present epoch, by more than one mile, which would give less than fifteen meters per year; whereas the real progress is at least four or five times more rapid…
“As a result, the frontal advance of the alluvia of the Mississippi appears to take place at the rate of one hundred meters per year, and of one mile every sixteen years, at least if one adheres to the average of one hundred and thirty years of hydrographic observations. Thus the river has been able, within the memory of man, to form a vast territory at the surface of the ground, and, through this work, to initiate us into the entire formation of its delta… It is therefore evident to us that the formation of this delta, like so many other physical facts that have been referred, but
without proofs, to a high antiquity, belongs nevertheless to recent times.1”
We shall not end this chapter without making an observation that appears important to us concerning the waters of the seas and the mineral and animal materials they contain. To calculate their depth, we have data that cannot depart greatly from the truth. The estimate made of it by Laplace in his Theory of the Tides fixes the average at four thousand meters: yet it has not been possible to touch the bottom, because the sounding lead always ends by floating, both because of the weight of the line, which finally prevails over that of the cylinder, and because of the increasing density of the liquid. What is this density of the seas at great depths? It would be impossible to say; but there is reason to think that it must be very considerable, if one judges by the density established at the surface and by the maximum depth of the Ocean, which is seven to eight thousand meters. According to all the data one possesses, it may be asserted without exaggeration that [the water] is found there in the state of mud, mixed with a great quantity of mineral, argillaceous, calcareous, siliceous substances, etc., with detritus of organized beings, and populated by those beings that are no longer found except among the fossils of sedimentary terrains.
And let the force of marine currents not be opposed to this accumulation of
materials; none of these currents, not even the great equatorial current, reaches the deep layers of the Ocean; their impulse is exerted at the surface or at shallow depths; the extremities of the abyss escape their action.
What is happening now in the Baltic Sea proves this assertion. It has been observed that, for centuries, the bottom of this sea has not ceased to rise, as a result of the constant deposit made there of a mass of tests and calcareous shells. This modern phenomenon, which we catch, so to speak, in the act, places before our eyes the positive explanation of the manner in which fossiliferous terrains were formed in the ancient world.
Let us now suppose that a violent earthquake or an immense volcano comes to raise the shoals of a sea—which has happened many times—and to displace its bed: is it not evident that these bottoms, thus emerged, formed of clay, limestone, and silica, and kneaded with organic debris, would constitute hills and fossiliferous mountains, whose terrains, pasty at first, would solidify and transform themselves into limestone, in a more or less long time, through the agglomeration of the enormous quantity of silica proceeding from the transudation of shell-bearing animals, which secrete much of it and whose number is prodigious? And what physicist will be able to maintain that, for operations of this kind, three or four thousand years would not suffice?
We also find in these uplifts of the seas the explanation of the phenomena presented to us by the upper beds of the lower Cretaceous terrains, whose limestones and sandstones, and even trees, are perforated by shipworms and pholads. It is evident that the work was done by these mollusks in marine deposits that some cause subsequently raised.
To corroborate our assessments on this subject, we shall cite the conclusions that the learned de Lamétherie drew from the simultaneous action of the igneous causes and the aqueous causes—which he regarded as synchronous with the former—for the formation of terrains, mountains, and valleys.
“If several flat beds are superposed,” he says, “and an internal force raises them and forms a mountain from them, they break; they everywhere present fissures and ruins, and will not present themselves in a vertical position over a great extent… It must therefore be acknowledged that most vertical or oblique beds were formed as they are… It is the same with contorted beds that are whole, without tearing.
“Let one observe,” he adds, “the deposits made by muddy waters; for example, those of rivers such as the Saône, the Seine, etc., whose waters, in times of their floods, are turbid and carry much clay, marl, and limestone; one will see that this clay, this marl, and this limestone
are deposited indiscriminately upon all sorts of terrains; and that these deposits are of the same thickness both in places whose surface is level and upon hillsides whose surface is inclined. Now, upon these latter hillsides, the deposits form conical beds. Let these facts be borne in mind, and one will easily conceive the formation of mountains.2”
We shall not enter into more ample developments; that is not our task. We do no more than indicate, in broad strokes, the causes that have contributed to the present structure of the globe. These causes have always acted; they still act, although with a much lesser intensity. Let them be studied without prejudices, without preconceived ideas, without prepossessions, with the conviction that therein lies the secret of the phenomena we observe, without having recourse to fantastic laws to explain what they do not explain. This is the candid admission that a partisan of the periods made to us recently, after a long discussion: “In the final analysis,” he said to us, “I believe that you are right. These periods, which were supposed to cast a vivid light upon the organization of the globe, in reality explain nothing!”