Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/45

Rh which is still to be reckoned as belonging to a continental slope. But even if we follow Koszmat and Andrée, who, for example, assume a depth of deposition of the Alpine radiolarite of 4 to 5 km., the space occupied by such oceanic deposits, compared with the extent of the continents, is still so small that the principle of the general permanence of the continental blocks is not at all damaged by it. The present continental blocks, with but trifling exceptions, have never in the history of the earth formed the floor of the ocean, but were, as at present, continental platforms. The conception of Lyell of a repeated submergence and emergence is thus limited, in that it only concerns the alternating shallow floodings of the permanent continental platforms.

But this gives rise to a great difficulty in the construction of bridging-continents where now oceans, exist. If their re-elevation were not compensated by an equivalent re-submergence in another place, the remaining much diminished ocean basins would not have nearly enough room for the total amount of water of the oceans. The re-elevation of those former continental bridges would raise the surface of the water so much that all the continents, old as well as new, with the exception of lofty mountains, would be completely flooded. In other words, the assumption of continental bridges does not lead to the desired end, which consists of a land connection between extended continents. In order to surmount this difficulty, which was emphasized by Willis and Penck, we must make the assumption, not otherwise warranted, and therefore improbable, that the water on the earth had increased proportionately at the same time as the continental bridges sank. But this hypothesis has not up to the present been seriously considered and championed. With the more probable assumption that the amount of water has remained