The transfer of matter from the exposed land surfaces to the sub-oceanic slopes of the continents and the increase in the density of the ocean, must all along have been attended by isostatic readjustment. We cannot take any other view. On the one hand the land was being lightened; on the other the sea was increasing in mass and depth and the flanks of the continents were being loaded with the matter removed from the land and borne in solution to the ocean. How important the resulting movements must have been may be gathered from the fact that the existing land of the Globe stands at a mean elevation of no more than 2,000 feet above sea level. We have seen that solvent denudation removed over 1,600 feet of rock. But we have no evidence that on the whole the elevation of land in the past was ever very different from what it now is. We have, then, presented to our view the remarkable fact that throughout the past, and acting with extreme 53 slowness, the land has steadily been melted down into the sea and as steadily been upraised from the waters. It is possible that the increased bulk of the ocean has led to a certain diminution of the exposed land area. The point is a difficult one. One thing we may without much risk assume. The sub-aereal current of dissolved matter from the land to the ocean was accompanied by a sub-crustal flux from the ocean areas to the land areas; the heated viscous materials creeping from depths far beneath the ocean floor to depths beneath the roots of the mountains which arose around the oceans. Such movements took ages for their accomplishment. Indeed, they have been, probably, continuous all along and are still proceeding. A low degree of viscosity will suffice to permit of movements so slow. Superimposed upon these movements the rhythmic alternations of depression and elevation of the geosynclines probably resulted in releasing the crust from local accumulation of strains arising in the more rigid surface materials. The whole sequence of movements presents an extraordinary picture of pseudo-vitality--reminding us of the circulatory and respiratory systems of a vast organism. All great results in our universe are founded in motions and forces the most minute. In contemplating the Cause or the Effect we stand equally impressed with the spectacle presented to us. We shall now turn from the great effects of denudation upon the history and evolution of a world and consider for a moment activities 54 so minute in detail that their operations will probably for ever elude our bodily senses, but which nevertheless have necessarily affected and modified the great results we have been considering.