THE argument from physics is just about as inconclusive as that from "geological evidence." He says:—
1. "Sir William Thompson, applying Fourier's theory of thermal conductivity, pointed out some years ago (1862) that in the known rate of increase of temperature downward and beneath the surface, and the rate of loss of heat from the earth, we have a limit to the antiquity of the planet. He showed, from the data available at the time, that the superficial consolidation of the globe could not have occurred less than twenty million years ago, . . . nor more than four hundred million years ago; . . . he inclines rather toward the lower than the higher antiquity, but concludes that the limit, from a consideration of all the evidence, must be placed within some such period of past time as one hundred million of years."
2. "The argument from tidal retardation proceeds on the admitted fact, that, owing to the friction of the tide-wave, the rotation of the earth is retarded, and is therefore much slower now than it must have been at one time. Sir William Thompson contends that had the globe become solid ten thousand million years ago, or indeed any high antiquity above one hundred million years, the centrifugal force due to the more rapid rotation must have given the planet a very much greater polar flattening than it actually possesses. He admits, however, that, though one hundred million years ago that force must have been about three per cent. greater than now, yet 'nothing we know regarding the figure of the earth and the disposition of land and water would justify us in saying that a body consolidated when there was more centrifugal force by three per cent. than now, might not now be in all respects like the earth, so far as we know it at present.'"
Thus, first, he contends that if the earth had become solid one hundred million years ago, it would have been much flatter at the poles than it is, yet is willing to admit that had it become solid then, we do not know but that it would have been now just as it is. Then if the result is the same in either case, where is the use of going back one hundred million years, or ten thousand million years, for the start? And so "Professor Tait concludes that this argument, taken in connection with the previous one, probably reduces the possible period which can be allowed to geologists to something less than ten millions of years." "What a falling off is there, my countrymen!" From ten thousand million to simply ten million! May we hope from this that they will finally reach the reasonable limit?
But Mr. Geikie has not yet exhausted his "argument" on the age of the earth; he presents his third from physics, thus:—
3. "The third argument, based upon the age of the sun's heat, is confessedly less reliable than the two previous ones."
But the "two previous ones" themselves are confessedly unreliable, and, if the third be admitted as "confessedly less reliable" than they, how much reliability has geological science for the age of the earth?
The secret, however, of the whole matter is exposed in his last remark on this subject:—
"One hundred million of years is probably amply sufficient for all the requirements of geology."
Yes, the geological ship has been launched upon the tide of speculation, and nothing less than one hundred million years will give her sea-room.
Next in order, we come to Part IV., Structural Geology—Order of Superposition—The Foundation of Geological Chronology:—
"As sedimentary strata are laid down upon one another in a more or less nearly horizontal position, the underlying beds must be older than those which cover them. This simple and obvious truth is termed the law of superposition."
Again, Part V., under "Use of Fossils:"—
"The true order of superposition is decisive of the relative ages of stratified rocks." "For geological purposes, therefore, and indeed for all purposes of comparison between the different faunas and floras of different periods, it is absolutely essential, first of all, to have the order of superposition of strata rigorously determined. Unless this is done, the most fatal mistakes may be made in Palæontological chronology."
And yet again, Part VI., No. 1:—
"In every stratigraphical research the fundamental requisite is to establish the order of superposition of the strata. Until this is accomplished, it is impossible to arrange the dates and make out the sequence of geological history."
This would be all plain and easy enough, if the rocks always and everywhere were lying in their true and original position. But in some places "the rocks composing huge mountain masses have been so completely overturned that the highest beds appear as if regularly covered by others which ought properly to underlie them."
Let us bring some of these statements together in the form of a parallel that we may more readily see their mutual bearing.
"The underlying beds must be older than those which cover them. This simple and obvious truth is termed the law of superposition." "The rocks comprising huge mountain masses have been so completely overturned that the highest beds appear as if regularly covered by others which ought properly to underlie them." In such instances "the apparent superposition may be deceptive."
So then "this simple and obvious truth" is not the truth. And then what becomes of the law of superposition? We rather incline to the opinion that it has been "completely overturned" as well as have been the mountain masses, and at the same time that they were. If, therefore, the apparent superposition may be deceptive, how are we to guard against deception? If huge mountain masses are lying in a directly inverted position to that of the valleys or the plains, how can we tell which is "upside down"? And how is the true order of superposition to be settled?
Just here the geologist's summum bonum, the fossil, comes in, thus:—
"It is by their characteristic fossils that the divisions of the stratified rocks can be most satisfactorily made. Each formation being distinguished by its own assemblage of organic remains, it can be followed and recognized even amid the crumplings and dislocations of a disturbed region."
Again:—
"But it is mainly by the remains of plants and animals imbedded in the rocks that the geologist is guided in unraveling the chronological succession of geological changes."
And further, one of the uses of fossils is plainly stated to be "to furnish a guide in geological chronology whereby rocks may be classified according to relative date, and the facts of geological history may be arranged and interpreted as a connected record of the earth's progress." From these statements it plainly appears that it is by the evidence of fossils that the "order of succession," or "superposition," or "relative age of strata" is made out.
Yet under "Relative Age of Fossils," is this equally plain statement:—
"The chronological sequence of fossils must be determined first of all by the order of superposition of their enclosing strata;" because "there is nothing in the fossils themselves, apart from experience, to fix their date."
Here are two statements that we wish to place side by side, that it may be seen what they really say. And what they do say, although it may appear surprising, can be sustained by a greater number of quotations than are here already given.
"It is mainly by the remains of plants and animals [fossils] imbedded in the rocks that the geologist is guided in unraveling the chronological succession of geological changes." "The chronological sequence [succession] of fossils [remains] must be determined first of all by the order of superposition [chronological succession] of their enclosing strata."
One of these says that the relative age of the rocks is determined by the fossils. The other says that the relative age of the fossils is determined by the rocks.
What is this but reasoning in a circle? Thus, for instance, the geologists say to us, "Here is a stratum of rock that was deposited fifty millions of years ago." But we ask, "How do you prove that?" They reply, "We prove it by the fact that in it are imbedded organic remains of the earliest forms of life that appeared on this planet." But again we ask, "How do you prove that to be 'the earliest form of life'?" The reply is, "We prove that by the simple fact of their being imbedded in that particular stratum of rock." Yes, certainly, prove each by the other, and they will then both be true. All this may be geological, but it assuredly is not logical, nor is it according to established rules of evidence.