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Rejection of Principles foreign to Analogy.
Of this, however, we may be most certainly convinced, that although, in any particular instance, we may fail in tracing out the real connexion of natural causes by this or that assumed analogy, which may in itself appear very conformable to probability, we shall assuredly never succeed by adopting any hypothesis which is independent of natural analogies, or foreign to them; we shall never arrive at any satisfactory explanation of nature, or any real philosophical truth, by having recourse to other principles Alien from those of induction. Nature must always be her own interpreter.
If we adopt hypotheses for example built upon metaphysical or moral considerations, we may be certain they will never conduct us to physical truth. Whatever may be their merits in themselves, and when directed to their proper purposes, they are totally misapplied in physical subjects: or rather, it must be from an entire misapprehension of the nature and objects of physical researches, that we shall ever be induced to connect them with such speculations.
Example: Theories of Cosmogony.
In the earlier stages of geological science it was in a singular degree abandoned, as it were, to groundless hypotheses, often framed in utter defiance of all principles of analogy. But a more just and rational method has since begun to prevail; a method which (whatever difference of opinion may exist on some points of detail) must be recognised by all philosophic inquirers, as sound in its principle, viz., that of reasoning cautiously on the facts, from the known to the unknown, by the guidance of rationally adopted analogies. Speculations, which, in accordance with some formerly received views, once passed current for sound geology, were really such as altogether to discredit the uniformity of natural causes. But the more closely we adhere to sober and legitimate induction, the more will every discovery indicate the unbroken uniformity of plan, which has prevailed through the immeasurable periods of past stages of organized life. "If," says Mr. Lyell, "instead of inverting the natural order of inquiry, we cautiously proceed in our investigations, from the known to the unknown, and begin by studying the most modern periods of the earth's history, attempting afterwards to decipher the monuments of more ancient changes, we can never so far lose sight of analogy as to suspect that we have arrived at a new system, governed by different physical laws*."
The necessity of proceeding on such principles, to the utter rejection of all gratuitous suppositions, or cherished prejudices, is now becoming more generally acknowledged: the grand conclusions deduced are
* Geology, vol. i. p. 160.
independent of all disputed theoretical questions; and are now admitted by rational geologists of all schools.
The evidence of facts is undeniable as to all the main features of the process by which the surface of our planet was gradually brought into its present condition. The business of inductive geology is to compare the monuments of early changes in the earth's surface with those now in the course of progress: and that this is a sound principle to proceed upon is assured to us by the circumstance, that in the succession of these changes we meet with no interruption: we witness such effects locally and gradually going on at the present day: we trace by diligent observation the evidences of their having gone on in the same manner (whether or not upon a larger scale) in ages earlier than the records of history: in the deposits characterized by the remains of organized beings of the same species as those now inhabiting the earth: in the earlier beds, where existing species are mixed with extinct: until we arrive in succession at those containing ljone of the former and all of the latter class. The continuance of the same set of appearances is unbroken from the present time, through those comparatively recent deposits, up to those of older formation. And though the authority of Cuvier was once appealed to as having inferred from the alternations in the tertiary formations of the Paris basin, that here there were interruptions of order, from causes not apparent, and that " the thread of induction was broken," yet the later researches of Lyell and others have explained those apparent breaches of continuity in the series, and the investigation of those tertiary beds, in all their varieties of organic characteristics, has now become the principal source of evidence by which geologists have fully established the unbroken series, the uninterrupted continuity of these formations, in relation with the existing organized products of the neighbouring seas, and the operations of now existing laws. And whatever may have been the magnitude of some of the operations in remote epochs, yet we find no deviation from the continuance of action of the same kind; no real suspension of regular laws, no simultaneous universal destruction and reconstruction of the globe; but through the whole range of those periods of which we can decipher the monuments, we have continued evidence of the same system of gradual changes by which the existing state of things was, by slow degrees, evolved out of previous orders of existence. Such must be the general view of the matter (whatever difference may subsist on minor points,) which will be upheld by the inductive geologist in contradistinction to the dogmatical assertions of the cosmogonist. The chimerical, yet favourite notion, of a sudden total change, of a catastrophe by which one world was suddenly reduced to chaos, and another as suddenly called forth out of its ruins, during any of the periods the records of which we read in their existing organic remains, is not only wholly inadmissible, inasmuch as it must be derived altogether from considerations alien to those of physical analogy, but is absolutely contradicted by all inductive testimony.
We find no period since the very commencement of all those depositions which contain organic remains, at which some portion of the earth's surface was not abundantly peopled with an animal and vegetable creation, more or less different indeed from that now existing, but in all respects preserving an exact uniformity of plan and design, and precisely and admirably fitted for the kind of existence which accorded with the then condition of the globe; but destined gradually to disappear as those conditions were changed, and as other and varied forms of existence were in succession introduced. The total absence of all marks of any universal sudden overwhelming convulsion, supplies positive proof that nothing of the kind took place within any of those periods, the monuments of whose duration we find in the accumulated remains of successive formations; especially during any of the later epochs, and least of all subsequently to the latest tertiary deposits, that is, within those times which can alone possibly accord with the received chronology of the human species, and with the aera of those changes which brought the globe into a state suited to the residence of man.
The adoption, then, of any such theory on which