Wide wave-cut terraces along the southern California coast are apparently in accord with the present stand of the sea and therefore must have been cut within the last few thousand years. Photographic comparisons, however, indicate that the erosion of rocky coasts has been negligible in the past 50 years even where the rocks are relatively soft shales. Narrow projecting points, stacks, and sea arches have suffered some erosion, but the straighter sections of rock cliffs look untouched. On the other hand, photographs and measurements indicate a retreat of unconsolidated formations on the open coast of as much as a foot per year. The erosion of unconsolidated materials near the Scripps Institution is going on at a decreasing rate judging from a comparison of three sets of measurements spaced over the past 28 years.

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