Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/40

16 mountains being only of subsidiary and more recent formation.” But how can these colossi of stone be explained by the contraction theory? It says that detached portions of the crust are left behind at the time of a general foundering and remain as steps or horsts under the action of the pressure due to arching. But no account is taken of the enormous areas which are affected thereby. This whole conception, already refuted theoretically by Hergesell, of a stationary and everywhere effective arching pressure in the outermost layers of the crust, is in absolute contradiction to the more recent and increasingly well-proven doctrine of isostasy or the flotation of the crust of the earth on a plastic lower shell.

The contraction theory, with its conception, due to Lyell, of a limitless alternation of the emergence of the deep sea floor above water and the submergence of the continents to the deep sea floor, is also in contradiction to the doctrine of the permanence of the oceans and continents. As will be shown later, we cannot completely admit this doctrine, but its arguments directed against the contraction theory are quite valid. From the standpoint of the universally admitted theory of isostasy, it appears to be physically impossible that a whole continent should sink such a large amount as 5 km. On the other hand, the marine deposits in the present continents show that these—with insignificant exceptions—were never deep sea areas, but were covered by the shallow seas of the continental shelves. In this way the contraction theory is refuted in a striking manner by the greatest features of the face of the earth.

The theory of the displacement of continents avoids all these difficulties. It permits the assumption of