Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/215

splitting of the blocks, for the first time in the Mesozoic and in places considerably later. The floor of the sea in front of them thus exhibits a relatively freshly exposed surface of sima, and must on that account be considered as relatively fluid. On these grounds it is not surprising that these coasts are isostatically compensated. Further, on account of this greater mobility of the sima, the continental margins experience only a slight resistance to displacement, and therefore become neither folded nor squeezed, so that neither marginal mountain chains nor volcanoes occur. Earthquakes are also not to be expected here, since the sima, by its power to flow, is mobile enough to render all necessary movements possible, without discontinuity. Expressed in an exaggerated manner, the continents act in this case as solid blocks of ice in fluid water.