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Page:Popular Science Monthly Volume 44.djvu/556

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THE POPULAR SCIENCE MONTHLY.

in the species, even without the aid of the physical changes which then took place, than are apparent in the species now existing. There is, in fact, no sufficient evidence either geological or biological to show the need of the long interval assumed. On the contrary, there is every reason to believe that it did not exist, but that palæolithic man and his companions came down to within some ten to twelve thousand years of our times. We can not suppose that either man or geological work would have remained stationary during seventy thousand years, and yet that is the conclusion we should be driven to adopt. Are we to be debarred from pursuing these inquiries by a hypothesis having no better foundation, and involving such unquestionable difficulties?

Another barrier to inquiry is the postulate which would fix the rate of upheaval of the land during geological periods upon observations based—not upon the experience of even two or three thousand years—but upon observations which do not extend beyond two centuries. These observations have shown, as put by uniformitarians, that the mean rate of elevation of the coasts of Norway and Sweden has been during that time two and a half feet in a century, and this scale has been accepted and employed unhesitatingly as a safe and sure basis for calculation of geological time. The determination of a secular rise of the land is of itself an interesting fact, as settling the question of a retained mobility in the earth's crust; but it is quite insufficient, even if it were applicable, to establish a definite rate, not only for the past but even for the present. It is not a mean rate that is wanted. No upheaval can be otherwise than local and graduated. The extremes are what is needful. No engineer would take the mean delivery of a river as the measure to be depended upon for a water supply. It is the limit in both directions, or the minimum and maximum quantities, that are essential. To know what earth movements can still effect, we should at least take the maximum rate, which amounts in the above case, at the North Cape, to five feet in the century, or double the measure of the mean adopted by uniformitarians.

If also, in calculating the present rate of elevation of the land, the mean rate along the whole length of the axis is adopted, the same rule should at least be applied to elevations of past periods, and the time should not be estimated by the height of any one point, as that may prove to be more or less in excess of the mean. Thus, for example, the Westleton marine shingle is found in Buckinghamshire at a height of six hundred feet. Estimating this upheaval at the rate of two and a half feet in a century, the uniformitarian would put in a claim for twenty-four thousand years. But this bed, as it trends eastward, is met with at gradually lower levels, until in Suffolk it falls to the sea level. A