admit and call for inquiry into the nature of the causes to which they can be referred.

The pursuit of this inquiry soon discloses the evidence and monuments of successive changes which have occurred in the state of the earth's surface. In the attempt to trace these to their causes, sound inductive geology recognises, of course, the same principle of referring to those which are both true, and sufficient to explain the phenomena. We cannot find true causes except in such as are really proved to exist, and found by experience to be in operation. The action of the waters on the land, (whether the continued power of the rivers and ocean, or the occasional force of inundations and torrents,) the subterranean force of earthquakes, and the external operation of volcanoes; the contractions and expansions which must accompany changes in the temperature of any considerable thickness of the earth's crust: these and the like are the real causes to which the sound geologist refers.

The accumulation of soil at the bottom of the waters, the imbedding of animal and vegetable remains in those depositions, the elevation of portions of land out of the sea, are operations really and continually going on. When, therefore, fossil remains of organized beings are found imbedded in rocks bearing also the marks of a similar mode of deposition, we refer to such operations as those just mentioned as true causes to explain the phenomena. And numerous series and successions of such depo

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sits, containing the remains of species now extinct, and, successively in the order of deposition, containing fewer of recent and more of extinct kinds, even to whole genera, classes, and orders of beings, call for the like reference to the continued action of similar causes through periods of countless duration.

And even if difference of opinion arise among geologists as to the rapidity with which such changes may have been effected, yet no sound inquirer refers to causes of different kinds; no one now dreams of the plastic power of nature moulding the semblances of organic remains in her sportive moods; nor of the simultaneous formation of the different strata with all their fossils in one confused mass, from which they subsided at once into their present positions.

The continent of Sweden is shown to have been slowly rising, by elevation in a mass, above the level of the Baltic, by a gradual, insensible movement, unattended by any violence or dislocation; the effect of some enormous subterranean pressure.

Here, then, is a true cause; it is also one which perfectly explains the phenomena presented by numerous other large districts of the earth; which, containing immense deposits of marine shells, must once have formed the bed of the sea, above which they are now elevated; and exhibiting an unbroken level, we infer were elevated gradually, and without disturbance, by similar slowly-acting subterranean

forces, as true causes, and sufficient to explain the phenomena.

In the tremendous earthquake which occurred on the coast of Chili in 1835, an eruption of a submarine volcano caused an enormous wave which swept over and entirely desolated a considerable tract of country. The geologist traces the marks of such sudden and violent local inundations in various parts of the earth at remote epochs. Here, then, we have a real cause which explains them. And if, in some instances, the effects appear to have taken place formerly upon a larger scale, still we are not departing from the nature of a real cause in supposing submarine eruptions of greater violence.

Thus, while no difference of opinion exists among rational geologists as to the propriety of attempting to explain the facts solely by reference to "true' causes, questions have, nevertheless, been, and may fairly be, agitated, as to the frequency or intensity with which such causes may have operated in remote periods; and whether we should with greater probability lean to the idea of brief eruptions of enormous violence, or of long-continued action of ordinary energy. Such questions are clearly matter of fair and philosophical discussion. But the important point to be borne in mind is, the distinction between such suppositions as those, and speculations which would refer the effects in question to other agency of a different kind, and which has not any connexion with the legitimate objects of inductive research.

The questions at issue between certain geological schools refer only to a difference in the degree, not in the kind, 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 primæval 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