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Show 86 UNIFORMI1'Y IN TilE gulating the changes of its surface, from the m~st re~ote eras to the present, than they at first imagined ... If, m th1s state of the science, they still despaired of r~cone1lmg e;ery class of 1 · 1 phenomena to the operatiOns of ordmary causes, geo ogwa . · f d'b'l' by straining analogy to the utmost hm1ts o ere 1 11ty, ewvee nm ight have expected, that the balan~e o.f prob ab ITlt y at least would now have been presumed to mchne .towards the identity of the causes. But, after repeated expenence of .the failure of attempts to speculate on different classe~ of geological phenomena, as belonging to a distinct ~rd~r of thmgs, each ne~. sect persevered systematically in the prmc1ples adopted by their predecessors. They invariably began, as .each new. pr~blem presented itself, whether relating to the ammate or mammate world to assume in their theories, that the economy of nature was formerly governed by rules quite independent of those now established. 'Vhether they endeavoured to account for the origin of certain igneous rocks, or to explain the for~es which elevated hills or excavated valleys, or the causes which led to the extinction of certain races of animals, they first pre· supposed an original and dissimilar order of nature ; and when at length they approximated, or entirely came round to an opposite opinion, it was always with the feeling, that they con· ceded what they were justified a priori in deeming improbable. In a word, the same men who, as natural philosophers, would have been greatly surprised to find any deviation from the usual course of Nature in their own time, were equally sur· prised, as geologists, not to find such deviations at every period of the past. . The Huttonians were conscious that no check could be gtven to the utmost licence of conjecture in speculating on the causes of geological phenomena, unless we can assume invariab~e constancy in the order of Nature. But when they asserted thts uniformity without any limitation as to time, they were con· sidered, by the majority of their contemporaries, to hav.e ~een carried too far, especially as they applied the same prmCiple to the laws of the organic, as well as of the inanimate world* • • Playfair, after admitting the extinction of some species, says, "The it~abi· tants of the globe, then, like all other parts of it, are subject to change. It lS not only the individual that perishes, but whole species, and even perhaps genera, ~e ex.tinguished.''-" A chango in the animal kingdom seems to be a pat·t of 1 e otYler of nature, o.nd is visible in instances to which human power cannot bave ex· tended."-lllustrations of the Iluttonian Theory, 9 413. ORDER OF NATURE. 87 V\.,.e shall first advert briefly to many difficulties which formerly appeared insurmountable, but which, in the last forty years, have been partially or entirely removed by the progress of science; and shall afterwards consider the objections that still remain to the doctrine of absolute uniformity. In the first place, it was necessary for the supporters of this doctrine to take for granted incalculable periods of time, in order to ~xpl~in the fo~mation of s~dimentary strata by ca~ses now m. dmrn~l action. The time which they reqmred theoretically, IS now granted, as it were, or has become absolutely requisite, to account for another class of phenomena brought to light by more recent investigations. It must always have been evident to unbiassed minds, that s~~cessi~e . strata, containing, in regular order of superpoSitiOn, d1stmct beds of shells and corals, arranged in families as they grow at the bottom of the sea, could only have been formed by slow and insensible degrees in a great lapse of ages; yet, until organic remains were minutely examined and spe.cificaUy determined, it was rarely possible to prove that the s~r1es of deposits met with in one country was not formed simultaneously with that found in another. But we are now able to determine, in numerous instances, the relative dates of sedim~ntary ~ocks in distant regions, and to show, by their orgamc re~ams, that they were not of contemporary origin, but formed m succession. We often find, that where an inter. ruption in the consecutive formation in one district is indicated by a sudden transition from one assemblage of fossil species to ~nother, the chasm is filled up, in some other district, by other lmportant groups of strata. The more attentively we study the European continent, the greater we find the extension of the whole series of geological formations. No sooner does the ~alendar appear to be completed, and the signs of a succession of physical events arranged in chronological order, than we are called upon to intercalate, as it were, some new periods of vast duration. A geologist, whose observations have been confined to England, is accustomed to consider the superior and newer groups of marine strata in our island as modern, and such they are, comparatively speaking; but when he has travelled through the Italian peninsula and in SiciJy, and has seen strata of more recent origin forming mountains several |