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Page:Popular Science Monthly Volume 44.djvu/558

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THE POPULAR SCIENCE MONTHLY.

dogmas which forbid any interpretation of the phenomena other than that of fixed rules which are more worthy of the sixteenth than of the nineteenth century. Instead of weighing the evidence and following up the consequences that should ensue from the assumption, too many attempts have been made—not unnaturally by those who hold this faith—to adjust the evidence to the assumption. The result has been strained interpretations framed to meet one point, but without sufficient regard for the others. We repeat that we would not for a moment contend that the forces of erosion, the modes of sedimentation, and the methods of motion, are not the same in kind as they have ever been, but we can never admit that they have always been the same in degree. The physical laws are permanent; but the effects are conditional and changing, in accordance with the conditions under which the law is exhibited.

Such are the barriers which seem to us seriously to retard the advance in one direction of an important branch of theoretical geology, while in another it is fronted by the stern rules of an apparently definite calculation.

We must ask to be forgiven if we can not accept the conclusions of physicists respecting the extreme rigidity of the earth and the immobility of the crust as conclusive. That the rigidity is now very great—as great, we will admit for argument's sake, as if the globe were of glass or steel—may be as asserted, but that conclusion can only be accepted in so far as it conforms to the facts of geology. Were the data on which the conclusion is based fixed and positive, like those on which the laws of gravitation and light are established, there would be nothing for the geologist to do but to bow to the decision of the physicist, and, if possible, revise his work. But in this case the tidal observations, on which the calculations of rigidity are mainly based, are of such extreme delicacy that, failing as the hypothesis does to satisfy the requirements of geology, the geologist may be excused for his dissent, pending further inquiry. Should this tend to confirm the extreme rigidity of the globe, we must seek for some explanation of earth movements consistent with that rigidity. It is indisputable that up to the latest geological period—that touching on our own times—the mobility of the crust was very considerable, for the raised beaches of Europe and of the Mediterranean prove conclusively that in that period extensive tracts were raised at intervals to heights of from ten to six hundred feet or more above their former levels. It is difficult to conceive that a globe, of which the crust was then so mobile, could have acquired, in the comparatively short interval between the latest of the beaches and our own time, so great a rigidity as to be practically immobile.

For similar reasons the conjoint conclusion that the crust of