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Again, the upheaving and laying dry from the domains of the ocean of any large portion of land, especially where it is destitute of all marks of forcible disruption, or the apparent effects of sudden violence, must, by rational comparison, be inferred to have taken place by almost imperceptible degrees. When we combine these considerations with that of the number of superposed beds which observation of the varieties of mineral character as well as of characteristic fossils discloses to us, and of the limited local extent of each, we are necessitated, upon the lowest possible computation consistent with inductive inference, to assign an almost incalculable series of ages to each one of those successive deposits, and, strictly in the spirit of inductive analogy, to carry our inferences back to epochs in the depths of primæval antiquity in the history of our planet, during which long-continued dynasties of animal and vegetable life maintained their sway under circumstances more or less different from any which prevail now, yet in all cases evincing the unbroken continuance of the same analogies in the structure and instincts of the animals, and in the regular operation of the same physical laws in conformity with which the changes were brought about.
Instances occur where a mountain mass bears evident marks of having been forced up from beneath, while, resting on its base, the strata of the plain (of a different kind of rock,) are observed perfectly horizontal and undisturbed. No one who is disposed to consider the subject in a rational way can doubt that these undisturbed strata were deposited after the upheaving of the mountains.
Again, in certain other mountains, a different set of appearances present themselves; patches of superficial strata, the same as those of the valley, are found resting on the elevated parts; and the strata of the valley also disturbed from their horizontal position, tilted up and inclined against the sides of the mountain. No reasonable doubt can be entertained that these were deposited before the upheaving of the mountains; and were carried up by the same action which elevated them.
Combinations of Inductions.
THE force of inductive conclusions, guided by wide analogies, is often immensely increased by the combination, and converging to a common point, of several different trains of investigation, setting out from entirely distinct and remote origins; yet all ultimately, and often very unexpectedly, brought to bear on the same conclusion.
Thus Dugald Stewart* had acutely observed, “ The uniformity of animal instinct presupposes a corresponding regularity in the physical laws of the universe, insomuch that if the established order of the material world were to be essentially disturbed, (the instincts of the brutes remaining the same,) all their various tribes would inevitably perish.” Mr.
* Philosophy of Mind, ii. 230.
Lyell extends this inference in a remarkable manner to the condition of the globe at a remote period.
“ Any naturalist,” (he observes,) “ will be convinced, on slight reflection, of the justice of this remark. He will also admit that the same species have always retained the same instincts, and therefore that all the strata wherein any of their remains occur must have been formed when the phenomena of inanimate matter were the same as they are in the actual condition of the earth. The same conclusion must also be extended to the extinct animals with which the remains of these living species are associated; and by these means we are enabled to establish the permanence of the existing physical laws throughout the whole period when the tertiary deposits were formed *.”
Geology, indeed, is full of striking examples of such combined inductions. It calls to its aid the separate resources of many distinct branches of physical inquiry, and from their united testimony, collects the materials of its conclusions.
Thus the naturalist traces not only the invariable characteristics of species, but also the peculiarities which mark the adaptation of species to climate; he finds the characteristics belonging to a warm climate in the fossil remains which the geologist submits to his examination.
The astronomer demonstrates the effects of the change which is taking place with insensible slow
ness in the form of the earth's orbit, to be that of a diminution (however slight,) in the mean temperature arising from the supply of heat from the sun..
While the physical philosopher argues on the theory of central heat for the primitive high temperature of the globe, the meteorological geographer finds in the peculiar distribution of land and water on the earth's surface, a powerful agent in modifying climate. The geologist infers from unequivocal proofs that such changes in the distribution of sea and land have actually occurred. And by successive local operations, extensive and ultimately perhaps universal alterations have been accomplished in the relative position of the oceans and continents. Such effects have gone on in former periods by depositions and inroads, by elevations and subsidences, as they are still continuing to do.
How vastly does the mutually-conspiring testimony of these very different trains of research tend to increase the force of the inductive inference that the fossil animals and plants alluded to existed at incalculably remote periods, when the present land was the bed of the ocean, and when the surface of our planet enjoyed a higher temperature than at present, and that from the changes of temperature and local conditions, causes were brought into action, which occasioned the extinction of some species, and were favourable to the introduction of others of new kinds.
Caution in assuming Analogies.
But even if in any case a particular analogy should fail; if the clue should break; if some unexpected and anomalous fact should throw into confusion our previously imagined arrangement, still so powerful is the confidence inspired by what we do satisfactorily know of the permanence of natural order, that we can never really distrust the stability of such a foundation for our reasonings.
If it be true that this particular analogy is overthrown, the only fair conclusion is, that, in this case, our conceptions were too hasty, not that the order of nature is violated. The conviction that some real analogy subsists is in no degree weakened, because we may have failed as yet to light upon it. The eertainty that there is a right path is not diminished because we may have taken a wrong one. The only effect of such an occurrence on a truly philosophic mind, will be the excitement of a still more diligent search after those characteristic circumstances which may indicate the true point of comparison.
We will illustrate this remark by a few examples:
(1.) The earth moves from west to east; all the primary planets revolve in the same direction, including Uranus; the same is true of our moon, and of those of Jupiter and Saturn, and the ring of the latter planet. On the discovery of the satellites of Uranus, would it not then have appeared fair to expect that they would move in the same direction?