Imágenes de página
PDF
ePub

of the materials of the recent strata, is proved by their constitution. Quartz, felspar, mica, and hornblende are the chief materials of the sandstone, shales, and clays ; nay, the very fragments of that rock are found everywhere. Even in our recent alluvial soils they abound ; and it is a question worth considering whether the granite boulders, of which the immediate origin has so often been vainly traced, are not rather the portions of decomposed conglomerate strata, or the more durable remains of the alluvial soils on which they now repose.”—Macculloch's Geology, vol. i., p. 155.

“He who shall divest the present surface of all but its rocks, who shall exterminate from our maps the great alluvial plains and deltas of the globe, with the countless interior tracts of the same nature, will produce a sketch of the original earth in no small degree interesting. It is through decomposition and disintegration, aided by mechanical power, that these changes have been produced.” -Macculloch's Geology, vol. ii. p. 2.

We shall have occasion in the course of the discussion to cite other passages in which the same views are presented. According to the theory, then, the continents from which the vast materials of the sedimentary strata were originally drawn, consisted throughout their whole mass of granite, and it was by the slow process of disintegration by the action of the atmosphere, heat, moisture, frost, rains, tor

rents, and rivers, that that generally hard and almost unyielding substance was reduced to fragments and minute particles, and transported to the sea.

The question now is, whether they have demonstrated these great postulates. It is not enough to authorize the stupendous inference they have grounded on them respecting the age of the world, and invest it with the character of a scientific deduction according “to the strictest rules of the Baconian philosophy," to show that they are possibly or even probably true. They, must be established by the most unanswerable evidence, in order that they can serve as a foundation for the vast fabric which is attempted to be erected on them. If they are mere suppositions, or gratuitous assumptions--if, instead of being demonstrated, they involve gross self-contradictions, and are irreconcilable alike with the laws of matter and the principles of geology, then the lofty structure which has been reared on them must be equally unsubstantial; and such we shall now proceed to show is their character.

The question which first requires consideration respects the sources from which the materials of the strata were drawn. And we remark in the first place that it is a mere hypothesis, not a demonstrated fact, that they were derived from continents, islands, or mountains that consisted exclusively of granite. These writers have not proved it. They do not even claim

to have demonstrated it. They have taken it for granted, or advanced it simply as a supposition that furnishes in their judgment a more probable explanation than any other of the formation of the primary crust of the earth, and of the origin of the materials of the strata that were subsequently imposed on the primitive rocks. Thus Dr. Buckland says:

“As the materials of the stratified rocks are in great degree derived directly or indirectly from those which are unstratified, it will be premature to enter upon the consideration of derivative strata until we have considered briefly the history of the primitive formations. We therefore commence our inquiry at that most ancient period, when there is much evidence to render it PROBABLE that the entire materials of the globe were in a fluid state, and that the cause of this fluidity was heat. .... ASSUMING that the whole materials of the globe may have once been in a fluid state, from the presence of intense heat, the passage of the first consolidated portion of this fluid to a solid state may have been produced by the radiation of heat from the surface into space ; the gradual abstraction of such heat would allow the particles of matter to approximate and crystallize; and the first result of this crystallization might have been the formation of a shell or crust, .... constituting various rocks of the granitic series.Bridgewater Treat., pp. 39, 40.

“Whence came the materials of the great mass of deposits which rest upon the primary gneiss and mica schist ? Probably the true answer to this, though we cannot now give adequate proof of it, is that the disintegration of granite and other igneous rocks, to which--on what seem good grounds—we have already ascribed the origin of gneiss and mica schist, has been the prolific source of all these sedimentary strata. Analysis of the principal rocks of the slaty systems does certainly not contradict this view ; which neither those who admit with Leibnitz the first solid covering of the globe to have been a mass of rocks cooled from fusion, or with Lyell that strata added above are melted and reabsorbed into granite below, have any reason to deny."Phillips's Geology, vol. i. p. 150.

This view of the primitive earth, which they make the basis of their theory of the formation of the strata and inference of the immense age of the world, is thus merely supposititious. It is not advanced as an ascertained and indubitable fact. It is not even held to be susceptible of demonstration. An attempt to verify it by “the strictest rules of the Baconian philosophy” would be regarded by geologists themselves as an extravagance. In its highest character it is only a conjecture. This consideration overturns, therefore, the deduction that is founded on it respecting the long existence of the world. That conclusion cannot be established on a mere hypothesis. It cannot rise any higher in certainty than the premise from which it is drawn. To build it, moreover, on such a basis, is as inconsistent with the principles of geology, as it is with the laws of logic; as they—as was shown in

a former chapter--forbid the assumption of any geological effect or condition of the earth as a ground of induction, that cannot be proved to have actually existed. The whole fancy, accordingly, of a scientific confutation by it of the inspired history of the creation, and demonstration that the earth has subsisted through a vast round of ages, is mistaken. The circumstance that the sacred narrative is at variance with an undemonstrated and undemonstrable supposition, is no proof that it is not consistent with fact.

In the next place, their theory of the formation of the granitic world, from which they represent the materials of the strata as derived, is altogether gratuitous also, and in contravention of the laws of matter. That theory is, as stated by Dr. Buckland in the passage already quoted from him, that the matter of the earth was, when created, “ in a fluid” or “nebulous state;" that is, in the form of gas, “ from the presence of intense heat;" and that it was by " the radiation of that heat into space" that “the particles" were allowed to approximate and crystallize. Mr. Macculloch also entertains the same view.

“The first condition of the earth which has been inferred, is that of a gaseous sphere ; while it is my business to state that the only evidence for this is derived from THE ANALOGY OF COMETS, itself rather more inferential than proved, as far as the study of these bodies has hitherto proceeded. But it

« AnteriorContinuar »