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The questions at issue between certain geological schools refer only to a difference in the degree, not in the hind, of action supposed. The case is essentially distinct from any chimera of universal catastrophes and convulsive paroxysms.
Volcanic action, in a single day, has been known to raise a hill of some hundreds of feet in height. The elevation of a mountain peak of as many thousands may be ascribed by one geologist to the sudden action of volcanic energy a thousand times as great; by another, to an equal force acting through a thousand days. The probable reasoning in support of either supposition, must be made out from concurrent circumstances. But the important point is, that in either case, the theorist is not departing from known analogies and real causes. The man who should contend that the volcanic appearance of the mountain, together with all the marks of upheaving and disruption, are delusive, and that the whole was formed at once out of primaeval chaos, exactly in its present condition, would be fairly divested of all claim to the title of a geologist, or of a rational inquirer.
The question respecting the explanation of geological phenomena solely by existing causes, seems, like many other controversies, to be in a great degree, dependent on the meaning of terms. It has been contended that we ought to appeal as much to unlimited force as to unlimited time. But it appears to me that the unlimited extension in time of the operation of known causes is an assumption essentially distinct from that of an unlimited extension in intensity, this last being precisely that which would place them beyond the limits of known and real causes. It is undoubtedly true that we know causes only by their effects, and must infer the magnitude of the cause from the nature of the effects witnessed; but the very question is, whether we are to derive this magnitude by the multiplication of the time or the force. And (unless where there is positive evidence of the suddenness of the effect from collateral circumstances,) the former is the method which alone seems to bring us within the dominion of known causes.
Again, even those theorists who have been most disposed to adopt the supposition of sudden and enormous paroxysms of volcanic and diluvial action in the earlier stages of the condition of the earth, have never supposed them as extending over more than certain limited regions of the earth at one time. In fact, all the changes of which we have evidence in past epochs, have been manifestly local. And the operation of existing causes is confined to a series of the like partial and local alterations. Thus no sound inductive geologist at the present day can admit anything like an universal simultaneous formation; nor find support for any theory of a sudden cosmogony, applying at once to the entire surface of the present dry land. One small portion after another has been successively elevated and peopled with vegetable and animal life; again, in the course of profoundly-adjusted changes, to be obliterated and overwhelmed, while another has been in progressive advance.
In all such cases, then, the observed fact or result is referred as a particular case or species to some real existing genus or class of natural operations, and not left as a peculiar anomalous event, sui generis, or referred to arbitrary agency.
Causes whose existence and operation is evinced by experience, are the "true" causes to which alone we can refer. Yet questions may fairly arise, and indeed must be carefully discussed, relative to the other condition of the case, viz., whether any particular causes so assigned are sufficient to explain the phenomena? If they are not, we then fall back on the truly philosophical maxim so admirably laid down by Mr. Lyell: "When we are unable to explain the monuments of past changes, it is always more probable that the difficulty arises from our ignorance of all the existing agents, or all their possible effects in an indefinite lapse of time, than that some cause was formerly in operation which has ceased to act."
Connexion of Causes.
Thus the consideration of a "real cause," in fact, involves the connexion of one train of causes with another. The cause is shown to apply independently to one set of phenomena; we refer another class to the same cause. Thus we enlarge our ideas of the connexion of physical phenomena; we trace not only one series of causes and effects, but many, and these not independent, but united by common principles. We perceive a union between extended orders of facts. We find not merely one relation established, but a communication opened, as it were, with a vast range of such relations; and many such channels of communication, widely ramifying in all directions. The great truths of the natural world are proclaimed, as it were, not merely by the accordant evidence of a few witnesses, but of a vast number; and with the increasing assurance, too, that as many more as we may summon, will all confirm each other's statement. And this not merely in one or a few points, but in connected trains of narrative; and again, not only in one or a few, but a great number of distinct narratives, all of which throw light upon, and corroborate each other; and the number and extent of which is increasing and accumulating without limit
Ideas of Efficient Carnation.
By such considerations as those now adduced, it appears to me that we obtain a view of the relation of physical cause and effect at once simple and satisfactory; divested of mystery, yet rising above the relation of a mere invariable "sequence" of facts. We find the connexion of causes and effects in the connexion of laws and principles, And in the most strictly philosophical view of the matter, we rationally extend our notion of physical causation beyond the bare circumstance of two consecutive phenomena, to the conviction of an intimate union between them: which is no other than that of the particular individual case with the more general law: of that law with some still more comprehensive principle: and of this, again, in its turn, with some yet more universal theory: thus establishing not merely sequences but reasons, not merely connexions but explanations.
We may thus safely admit that our persuasion of an intimate causality (if rationally explained) is really something more than the mere influence of an ill-regulated imagination improperly intruding itself upon philosophical speculation. We thus sufficiently account for the most powerful conviction of a hidden connexion between natural events, which we experience even before the grounds of it have been distinctly analysed. In the successively higher generalizations which really constitute what is so improperly represented by the common metaphor of the "chain" of causes, we find a real and rational gratification of our longing anxiety to penetrate beyond the bare surface of sensible phenomena into the more hidden relations and mysterious combinations of nature.
If further confirmation of this view of the matter be wanting, we may find it in observing the dependence which the strength of our impression of an