Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/44

20 another solution by horizontal displacement was certainly not considered. As Ubisch emphasizes, the displacement theory will fit these requirements just as well as the present-day assumption of sunken intervening continents, indeed even better, because the close affinity of their faunas and floras would still appear rather mysterious on account of the present great distance from each other of these existing continents, even if an exchange of forms was at an earlier date possible over an intervening continent.

The arguments of the opposing doctrine of the permanence of continents and oceans rest not on biological but on geophysical grounds, and are directed essentially not against the former existence of land connections, but only against that of bridging-continents. The first argument consists in the facts already touched on, that on the continents deep-sea deposits do not occur to any considerable extent, so that the continental blocks as such are undoubtedly “permanent.” Strata taken earlier to be abyssal deposits have been found to be shallow-water sediments—as, for example, Cayeux demonstrated for the Chalk. For a very small number, such as the practically non-calcareous ‘radiolarites’ of the Alps and certain red clays which are reminiscent of the red abyssal clays, a great depth of origin is still assumed mainly because the sea-water acts as a solvent on the calcareous material only at great depths. The interpretation of these discoveries is, to be sure, still disputed, and it is believed that many are deposited at a depth of 1 to 2 km.,