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Page:Popular Science Monthly Volume 56.djvu/451

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A CENTURY OF GEOLOGY I.

accordance with the known geological history of the earth. If so, then the oceanic basins have always been oceanic basins, and the places of the continents have always been substantially the same. This introduces a subject on which there has been much discussion recently—viz.:

The Permanency of Ocean Basins.—Closely associated with the Lyellian uniformitarianism was the doctrine of extreme instability of earth features, especially the forms and places of sea and land. Crust movements were irregularly oscillating to such a degree that in the course of geologic history sea and land frequently and completely changed places. Abundant evidence of this was supposed to be found in the unconformities so frequent in the stratified series. The tendency of that time was toward a belief in up-and-down movements, back-and-forth changes, without discoverable, law, rather than progressive onward movement. On first thought it might seem that such lawless movement was rather in keeping with catastrophism than uniformitarianism. But not so, for the movements are supposed to be very slow. Again, it might seem on first thought that gradual progressive change—in a word, evolution—would be peculiarly in accord with uniformitarian ideas. But again not so, because this doctrine was, above all, a revulsion from the idea of supernatural purpose or design or goal contained in catastrophism. Uniformitarianism strongly inclined toward purposelessness, because of its supposed identity with naturalism. Thus for a long time, and still with many geologists, the tendency is toward a belief in irregular movements without discoverable law, toward instability of even the greatest features of the earth—viz., sea basins and continental arches. Geology for them is a chronicle, not a life history.

The contrary movement of thought may be said to have commenced with Dana. Dana studied the earth as a unit, as in some sense an organism developing by forces within itself. The history of the earth is a life history moving progressively toward its completion. The forces originating oceanic basins and continental arches still continue to deepen the former and enlarge the latter. From this point of view, oceanic basins and continental arches must have always been substantially in the same places. Oscillations there have been at all times and in all places, but they affect mainly the outlines of these great features, though sometimes affecting also the interior of continents and mid-sea bottoms, but not sufficiently to change greatly their general form, much less to interchange their places.

Such is the doctrine of permanency of oceanic basins. It is undoubtedly a true doctrine, but must not be held in the rigid