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are composed of earths or of minerals, and of animal and vegetable matters compacted. They are compacted by mechanical approximation, or by chemical action, or by both united.

ACTIONS.

"Actions are the results of animal and vegetable life and destruction, of water and the force of gravity, or of fire. By organic production and destruction its objects become portions of the fragments, or form strata, or parts of these. By water and gravity the solid rocks are broken into fragments, and deposited on the land or beneath the water. By water animal remains are mineralized, and vegetable ones bituminized. Fire acts in volcanoes which are visible or invisible. It elevates the superincumbent materials of the earth, whether solid or otherwise.

RETROSPECT.

"The inferences from objects and actions connect the present with the past. The fragments and solution of former rocks and earths in former water, produced the present stratified rocks. The effects of former fire produced the unstratified rocks with the consequences attributed to them. Former races of living animals and vegetables in different waters and on different lands, produced the objects of this nature now found in rocks and fragments. The successive connexions of distinct parallelisms among the stratified rocks infer as many distinct conditions of the globe. The time requisite for the production of stratified rocks, and for the reproduction of animals and vegetables, implies long intervals between each condition.

"With respect to the future, it is inferred that the present actions are tending to produce a new condition analogous to that which is just past."—/. Macculloch's Geol. vol. i. pp. 11-15.

"A practical observer . . . needs no labored argument to satisfy him that if the stratified rocks were deposited in the manner the work is now going on, immense periods of time were requisite. Even if he admit, what we are not disposed with some geologists to deny, that the causes now in operation did formerly act with greater energy than at present; yet he will still see the necessity of allowing periods of time vastly extended to form the fossiliferous rocks, unless he admit without proof that the laws of nature have been changed." Hitchcock's Geology and Revelation, p. 20.

Some geologists hold the necessity of regarding the rate at which those causes are now generating their several effects, as the measure of the rapidity with which they produced them at all former periods as so imperative, that to deny it were to strike from our hands all means of reasoning respecting them.

"All agree that the deposition of thick beds of limestone or clay replete with the exuviae of successive generations of marine or terrestrial animals, interrupted too by several periods of convulsion, during which the existing races were in many cases destroyed, and new ones afterwards substitnted, could not have been accomplished, consistently with the present laws of nature, within a very short space of time. And if it be said that the processes which produced them may be imagined to have proceeded at a more rapid rate, and in a different manner at that period, than they do at present, we reply, that such a supposition would strike at the root of every species of evidence; for if the author of nature should have imparted to the constituents of the globe those characters and relations which at the present time would result from the operation of known causes continued during a period of at least a certain duration, and yet have chosen to employ other agencies, of whose character and laws we know nothing, or have accomplished the whole by the immediate fiat of his omnipotence, there then is an end to all reasoning on the subject."—Literary Gazette, 1834, p. 771*

They thus unite first in maintaining that geology treats simply of the materials of which the crust of the earth consists, and of the forces from which they received their present form; and next, in regarding the effects which they attempt to explain, as not only produced by the chemical and mechanical forces

* He thus assumes that the causes to which the strata are to be referred, cannot have acted on any larger area, nor with any higher energy, than they now do; and that to suppose " the processes" to have taken place at a more rapid rate than at present, is to suppose that they were produced either by agencies of whose character we know nothing, or by the fiat of omnipotence; a mistake as obvious and absurd as it were to maintain that there can be no diversity in the strength and activity of chemical and mechanical forces.

that are now giving birth to somewhat similar changes on the earth's surface, but by agencies of essentially the same energy as those which they are now exerting.

Geology, it is thus seen from these statements of its objects, is not a demonstrative science. It is not a system of principles or laws by which a share of the great processes of nature are explained, and can, like the movements of the bodies of the solar system, be made the subject of exact calculation, and traced back through the past, or forward to the future. Instead, it is a mere statement or description of the stratified and other rocks which compose the crust of the globe, with a reference of them to the agents by which they are supposed to have been produced. It has no axioms or principles that are peculiar to itself, as the laws of optics are to light, and of gravity and motion to the phenomena of the solar system. In chemistry, experiments are made by which it is ascertained what substances have such an affinity for each other as to enter into combination; what the circumstances are in which their attractive powers act, what the proportions are in which they unite, and what the forms are which they assume. In like manner experiments have been made with bodies dropped from a height, and projected into the atmosphere, by which it has been ascertained what the motions are of bodies in space acted on by gravity, and by gravity and a projectile force; and the laws of those motions taken as indicating the laws of all material bodies moving in space, have been generalized and employed in the solution of the movements of the bodies of the solar system. But no analogous experiments are made in geology, by which it is ascertained from what quarter materials must be drawn to form such strata as those of which the transition, carboniferous, and tertiary systems consist, or what the periods are which are required for their formation. No laws, consequently, can be deduced from the strata themselves by which it can be demonstrated, that vast periods have been employed in their deposition. They present no data from which that conclusion can be scientifically deduced. If drawn at all as a logical conclusion from a premise, it must be from an assumption or hypothesis, not from an ascertained fact or demonstrated law of such formations.

Geology, indeed, has no axioms, or generalized facts whatever, except those, first, which respect the materials of which the different strata of the earth consist; secondly, the relations which they sustain to each other, or the order in which they are superimposed; and, thirdly, the agents or media through which they were formed and placed in their present positions; and they furnish no means of a scientific demonstration of a different and higher class of truths, such as the existence of the world through an

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