The alternation of periods of crustal deformation with periods of quiescence has frequently been noticed, and has been termed the “geological rhythm.” It may be attributed to the gradual accumulation of small strains during a quiescent period until the breaking point is reached, when earth-movements take place until equilibrium is restored, when the process is repeated. The gradual erosion of the land by river and wave-action and the consequent shifting of the load provides a certain amount of stress; but this is local, and calls for local readjustments only. A more generally effective agency may be the gradual slowing down of the earth’s rotation under the influence of tidal friction. The mechanism of this process was described by A. E. H. Love (“Nature,” 94, 1914, p. 254): “The surface of the ocean, apart from waves and tides, is at any time a figure of equilibrium answering to the speed of rotation at the time, more oblate when the speed is greater, less oblate when it is slower. Let us imagine that the lithosphere also is at some time a figure of equilibrium answering to the speed of rotation at that time. If the speed remained constant, the lithosphere would retain this figure, and the matter within it would remain always in the same configuration without having to support any internal tangential stress. Now suppose that the speed of rotation gradually diminishes. The surface of the ocean will gradually become less and less oblate. The lithosphere also will gradually become less oblate, but not to such an extent as to make it a figure of equilibrium answering to the diminished speed of rotation, while the matter within it will get into a state of gradually increasing internal tangential stress. The effect on the distribution of land and water will be that the depth of the ocean will gradually diminish in lower latitudes and increase in higher latitudes, the latitudes of no change being 35° 16′ N. and S. “The internal tangential stress in the matter within the lithosphere may increase so much that it can no longer be supported. If this happens a series of local fractures will take place, continuing until the lithosphere is again adjusted much more nearly to a figure of equilibrium, which will be less oblate than the original figure. The effect on the distribution of land and water will be that the depth of the ocean will increase rather rapidly and spasmodically in lower latitudes and diminish in higher latitudes. “Accordingly, the kind of geological change which the theory of tidal friction would lead us to expect is a sort of rhythmic sequence, involving long periods of comparative quiescence, marked by what Suess calls ‘positive movements of the strand,’ in the higher latitudes, and ‘negative movements’ in the lower, alternating with comparatively short periods of greater activity, marked by rise of the land around the poles and subsidences in the equatorial regions.”