History of the Intellectual Development of Europe, Volume II (of 2) / Revised Edition

by John William Draper

Not only were evidences thus offered of the existence of a high temperature, and, therefore, of the lapse of a long time by the present circumstances of the globe; every trace of its former state, duly considered, yielded similar indications, the old evidence corroborating the new. And soon it appeared that this would hold good whether considered in the inorganic or organic aspect.

Inorganic proofs of a former high temperature. In the inorganic, what other interpretation could be put on the universal occurrence of igneous rocks, some in enormous mountain ranges, some ejected from beneath, forcing their tortuous way through thus resisting superincumbent strata; veins of [303] various mineral constitution, and, as their relations with one another showed, veins of very different dates? What other interpretation of layers of lava in succession, one under another, and often with old disintegrated material between? What of those numerous volcanoes which have never been known to show any signs of activity in the period of history, though they sometimes occur in countries like France, eminently historic? What meaning could be assigned to all those dislocations, subsidences, and elevations which the crust of the earth in every country presents, indications of a loss of heat, of a contraction in diameter, and its necessary consequence, fracture of the exterior consolidated shell along lines of least resistance? And though it was asserted by some that the catastrophes of which these are the evidences were occasioned by forces of unparalleled energy and incessant operation—unparalleled when compared with such terrestrial forces as we are familiar with—that did not, in any respect, change the interpretation, for there could have been no abrupt diminution in the intensity of those forces, which, if they had lessened in power, must have passed through a long, a gradual decline. These necessarily imply long time. In that very decline there thus spontaneously came forth evidences of a long lapse of time. The whole course of Nature satisfies us how gradual and deliberate are her proceedings; that there is no abrupt boundary between the past and the present, but that the one insensibly shades off into the other, the present springing gently and imperceptibly out of the past. If volcanic phenomena and all kinds of igneous manifestations—if dislocations, injections, the intrusion of melted material into strata were at one time more frequent, more violent—if, in the old times, mundane forces possessed an energy which they have now lost, their present diminished and deteriorated condition, coupled with the fact that for thousands of years, throughout the range of history, they have been invariably such as we find them now, should be to us a proof how long, how very long ago those old times must have been.

Thus, therefore, was perceived the necessity of co-ordinating the scale of time with the scale of space, and such views of the physical history of the earth were [304] extended to celestial bodies which were considered as having passed through a similar course. In one, at least, this assertion was no mere matter of speculation, but of actual observation. Support from astronomical facts. The broken surface of the moon, its volcanic cones and craters, its mountains, with their lava-clad sides and ejected blocks glistening in the sun, proved a succession of events like those of the earth, and demonstrated that there is a planetary as well as a terrestrial geology, and that in our satellite there is evidence of a primitive high temperature, of a gradual decline, and, therefore, of a long process of time. Perhaps also, considering the rate of heat-exchange in Venus by reason of her proximity to the sun, the pale light which it is said has been observed on her non-illuminated part is the declining trace of her own intrinsic temperature, her heat lasting until now.

Astronomical facts imply slow secular changes.If astronomers sought in systematic causes an explanation of these facts if, for instance, they were disposed to examine how far changes in the obliquity of the ecliptic are connected therewith—it was necessary at the outset to concede that the scale of time on which the event proceeds is of prodigious duration, this secular variation observing a slow process of only 45·7'' in a century; and hence, since the time of Hipparchus, two thousand years ago, the plane of the ecliptic has approached that of the equator by only a quarter of a degree. Or if, again, they looked to a diminishing of the eccentricity of the earth's orbit, they were compelled to admit the same postulate, and deal with thousands of centuries. Under whatever aspect, then, the theory was regarded, if once a former high temperature were admitted, and the fact coupled therewith that there has been no sensible decline within the observation of man, whether the explanation was purely geological or purely astronomical, the motion of heat in the mass of the earth is so slow, yet the change that has taken place is so great, the variations of the contemplated relations of the solar system so gradual—under whatever aspect and in whatever way the fact was dealt with, there arose the indispensable concession of countless centuries.

To the astronomer such a concession is nothing [305] extraordinary. It is not because of the time required that he entertains any doubt that the sun and his system accomplish a revolution round a distant centre of gravity in nineteen millions of years, or that the year of epsilon Lyræ is half a million of ours. He looks forward to that distant day when Sirius will disappear from our skies, and the Southern Cross be visible, and Vega the polar star. He looks back to the time when gamma Draconis occupied that conspicuous position, and the builders of the great pyramid, B. C. 3970, gave to its subterranean passage an inclination of 26° 15´, corresponding to the inferior culmination of that star. He tells us that the Southern Cross began to be invisible in 52° 30´ N., 2900 years before our era, and that it had previously attained an altitude of more than 10°. When it disappeared from the horizon of the countries on the Baltic, the pyramid of Cheops had been erected more than a thousand years.

Proofs of time from aqueous effects,We must pass by a copious mass of evidence furnished by aqueous causes of change operating on the earth's surface, though these add very weighty proof to the doctrine of a long period. The filling up of lakes, the formation of deltas, the cutting power of running water, the deposit of travertines, the denudation of immense tracts of country, the carrying of their detritus into the sea, the changes of shores by tides and waves, the formation of strata hundreds of miles in length, and the imbedding therein of fossil remains in numbers almost beyond belief, furnished many interesting and important facts. Of these not a few presented means of computation. It would not be difficult to assign a date for such geographical events as the production of the Caspian and Dead Seas from an examination of the sum of saline material contained in their waters and deposited in their bed, with the annual amount brought into them by their supplying rivers. Such computations were executed as respects the growth of Lower Egypt and the backward cutting of Niagara Falls, and, though they might be individually open to criticism, their mutual accordance and tendency furnished an evidence that could not be gainsaid. The continual accumulation of such evidence ought not to be without its weight on those who are still disposed to [306] treat slightingly the power of geological facts in developing truth.

and from the movements of the earth's crust.To such facts were added all those, with which volumes might be filled, proving the universality of the movements of the solid crust of the earth—strata once necessarily horizontal now inclined at all angles, strata unconformable to one another—a body of evidence most copious and most satisfactory, yet demonstrating from the immensity of the results how slowly the work had gone on.

How was it possible to conceive that beds many hundred feet in thickness should have been precipitated suddenly from water? Their mechanical condition implied slow disintegration and denudation in other localities to furnish material; their contents showed no trace of violence; they rather proved the deposition to have occurred in a tranquil and quiet way. What interpretation could be put upon facts continually increasing in number like those observed in the south-east of England, where fresh-water beds a thousand feet thick are covered by other beds a thousand feet thick, but of marine origin? What upon those in the north of England, where masses once uplifted a thousand feet above the level, and, at the time of their elevation, presenting abrupt precipices and cliffs of that height, as is proved by the fractures and faults of the existing strata, have been altogether removed, and the surface left plain? In South Wales there are localities where 11,000 feet in thickness have been bodily carried away. Whether, therefore, the strata that have been formed, and which remain to strike us with astonishment at their prodigious mass, were considered; or those that have been destroyed, not, however, without leaving unmistakable traces of themselves; the processes of wearing away to furnish material as well as the accumulation, of necessity required the lapse of long periods of time. The undermining of cliffs by the beating of the sea, the redistribution of sands and mud at the bottom of the ocean, the washing of material from hills into the lowlands by showers of rain, its transport by river courses, the disintegration of soils by the influence of frost, the weathering of rocks by carbonic acid, and the solution of limestone by its aid in water—these are effects [307] which, even at the quickest, seem not to amount to much in the course of the life of a man. A thousand years could yield but a trifling result.

We have already alluded to another point of view from which these mechanical effects were considered. The level of the land and sea has unmistakably changed. There are mountain eminences ten or fifteen thousand feet in altitude in the interior of continents over which, or through which shells and other products of the sea are profusely scattered. And though, considering the proverbial immobility of the solid land and the proverbial instability of the water, it might at first be supposed much more likely that the sea had subsided than that the land had risen, a more critical examination soon led to a change of opinion. Before our eyes, in some countries, elevations and depressions are taking place, sometimes in a slow secular manner, as in Norway and Sweden, that peninsula on the north rising, and on the south sinking, at such a rate that, to accomplish the whole seven hundred feet of movement, more than twenty-seven thousand years would be required if it had always been uniform as now. Elsewhere, as on the south-western coast of South America, the movement is paroxysmal, the shore line lifting for hundreds of miles instantaneously, and then pausing for many years. In the Morea also, range after range of old sea cliffs exist, some of them more than a thousand feet high, with terraces at the base of each; but the Morea has been well known for the last twenty-five centuries, and in that time has undergone no material change. Again, in Sicily, similar interior sea-cliffs are seen, the rubbish at their bases containing the bones of the hippopotamus and mammoth, proofs of the great change the climate has undergone since the sea washed those ancient beaches. Italy, pre-eminently the historic country, in which, within the memory of man, no material change of configuration has taken place since the Pleistocene period, very late geologically speaking has experienced elevations of fifteen hundred feet. The seven hills of Rome are of the Pliocene, with fluviatile deposits and recent terrestrial shells two hundred feet above the Tiber. There intervened between the older Pliocene and the newer a period of enormous length, as is [308] demonstrated by the accumulated effects taking place in it, and, indeed, the same may be said of every juxtaposed pair of distinctly marked strata. It demanded an inconceivable time for beds once horizontal at the bottom of the sea to be tilted to great inclinations; it required also the enduring exertion of a prodigious force. Ascent and descent may be detected in strata of every age: movements sometimes paroxysmal, but more often of tranquil and secular kind. The coal-bearing strata, by gradual submergence, attained in South Wales a thickness of 12,000 feet, and in Nova Scotia, a total thickness of 14,570 feet; the uniformity of the process of submergence and its slow steadiness is indicated by the occurrence of erect trees at different levels: seventeen such repetitions may be counted in a thickness of 4515 feet. The age of the trees is proved by their size, some being four feet in diameter. Round them, as they gradually went down with the subsiding soil, calamites grew at one level after another. In the Sidney coal-field fifty-nine fossil forests thus occur in superposition.

Organic proofs of a former high temperature.Such was the conclusion forcing itself from considerations connected with inorganic nature. It received a most emphatic endorsement from the organic world, for there is an intimate connexion between the existence and well-being both of plants and animals, and the heat to which they are exposed. Why is it that the orange and lemon do not grow in New York? What is it that would inevitably ensue if these exotics were exposed to a cold winter? What must take place if, in Florida or other of the Southern states, a season of unusual rigor should occur? Does not heat thus confine within a fixed boundary the spread of these plants? And so, again, how many others there are which grow luxuriantly in a temperate climate, but are parched up and killed if fortuitously carried beneath a hot tropical sun. To every one there is a climate which best suits the condition of its life, and certain limits of heat and cold beyond which its existence is not possible.