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Show 382 CONCLUDING R'EMARI{S. [Cl1, XXVI. cessive periods, has extended over a subterranean space equal at least in area to the present European continent, and often through a portion of the earth's crust 4000 feet or more in thickness. The principal effect of these volcanic operations in the nether regions, during the tertiary periods, or since the existing species began to flourish, has been to heave up to the surface hypogene formations of an age anterior to the carboniferous. We imagine that the repetition of another series of movements, of equal violence, might upraise the plutonic and metamorphic rocks of many of the secondary periods ; and if the same force should still continue to act, the next convulsions might bring up the tertiary and recent hypogene rocks, by which time we imagine that nearly all the sedimentary strata now in sight would either have been destroyed by the action of water, or would have assumed the metamorphic structure, or would have been melted down into plutonic and volcanic rocks. At the close of this chapter the reader will find a table of the chronological relations of the principal divisions of rocks according to the views above set forth. The sketch is confessedly imperfect, but it will elucidate our theory of the connexion which may exist between the hypogene rocks of different periods, and the alluvial, volcanic, and sedimentary formations. A second table is added, containing the names of some of the principal groups of sedimentary strata mentioned in this work, arranged in their order of superposition. Concluding Remarlcs.-In our history of the progress of geology, in the first volume, we stated that the opinion originally promulgated by Hutton, ' that the strata called primitive were mere altered sedimentary rocks,' was vehemently opposed for a time, the main objection to the theory being its supposed tendency to promote a belief in the past eternity of our planet. Previously the absence of animal and vegetable remains in the so-called primitive strata, had been appealed to, as proving that there had been a period when the planet was uninhabited by living beings, and when, as was Ch. XXVI.] CONCLUDING REMARKS, 383 also inferred, it was uninhabitable, and, therefore, probably in a nascent state. The opposite doctrine, that the oldest visible strata might be the monuments of an antecedent period, when the animate world was already in existence, was declared to be equivalent to the assumption, that there never was a beginning to the present order of things. The unfairness of this charO'e was clearly pointed out by Playfair, who observed, 'that 0 it was one thing to declare that we had not yet discovered the traces of a beginning, and another to deny that the earth ever had a beginning.' We regret, however, to find that the bearing of our arguments in the first volume has been misunderstood in a similar manner, for we have been charged with endeavourinO' to establish the proposition, that ' the existing causes of ch;1ge have operated with absolute uniformity from all eternity*.' It is the more necessary to notice this misrepresentation of our views, as it has proceeded from a friendly critic whose theoretical opinions coincide in general with our own, but who has, in this instance, strangely misconceived the scope of our argument. With equal justice might an astronomer be accused of asserting, that the works of creation extend throuO'hout infinite space, because he refuses to take for granted th=t the remotest stars now seen in the heavens are on the utmost verge of the material universe. Every improvement of the telescope has brought thousands of new worlds into view, and it would, therefore, be rash and unphilosophical to imagine that we already survey the whole extent of the vast scheme, or that it will ever be brought within the sphere of human observation. But no argument can be drawn from such premises in favour of the infinity of the space that has been filled with worlds · and if the material universe has any limits, it then follows that' it must occupy a minute and infinitessimal point in infinite space. So, if in tracing back the earth's history, we arrive at the monuments of events which may have happened millions of ages * Qual'tedy Review, No. 86, Oct. 18301 p. 464. |