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Page:Popular Science Monthly Volume 44.djvu/557

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543
THE POSITION OF GEOLOGY.

mean of three hundred feet should therefore be taken, with a corresponding shorter time-term of twelve thousand years; or are we to ignore any interval of time and to look only at the beds on the coast where they are consecutive? From every point of view such estimates must be worthless.

More than this, the very leaders of the belief that the average rate of motion does not exceed that above named allow that "the average rate proposed is a purely arbitrary and conjectural one." It is admitted also that it is not improbable that during the last four hundred years there has been a still faster rate in high northern latitudes. Not only, however, is the half measure adopted, but the warning that higher measures exist is neglected. When therefore the mean is applied to determine the length of time required to effect such elevations as that of the marine shell bed on Moel Tryfaen, fourteen hundred feet above sea level and of late Quaternary age, uniformitarians are obliged to ask for a term of fifty-six thousand if not eighty thousand years. Should the case of Moel Tryfaen be objected to as uncertain, there are still the unquestioned raised beaches of Norway and Sweden, which are from two hundred to six hundred feet above the sea level, and of still more recent date. These, on the same estimate, would have taken for their upheaval some eight thousand to twenty-four thousand years. We need not, however, pursue this subject further. The very admissions of the advocates of tho two above-named measures of time, based upon present rates of denudation and of elevation, show how untenable their conclusions are.

Such observations, howsoever useful and suggestive, are in fact futile so far as regards their application to former rates of upheaval, and needlessly play with time. If we could suppose that the causes which produced those movements had' always acted with the same degree of energy, the reasoning would hold good; but, as that regularity depends upon the stresses to which the earth's crust has been exposed at any particular time, the effects must have varied in proportion as the stresses varied. With a cooling globe it could not have been otherwise. What those movements of the past were, and what their duration, must therefore be judged of by other circumstances and on surer data.

We trust we have now said enough to show upon how insecure a basis the uniformitarian measures of time and change stand. They have probably done more to impede the exercise of free inquiry and discussion than any of the catastrophic theories which formerly prevailed. The latter found their own cure in the more accurate observation of geological phenomena and the progress of the collateral sciences; but the former hedge us in by