Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/231

 extended polar wanderings (movement of the South Pole from the Lower Carboniferous to Permian from Central Africa to Australia in its then position, and movement of the North Pole from the Lower Tertiary to the Quaternary from the Aleutian Islands to Greenland).

As already mentioned, the question as to the forces which have caused and now cause the continental displacements is still too much in a state of flux to permit of a complete answer satisfactory in every detail. One thing may be taken as certain: continental displacements, folding and rifting, vulcanicity, the alternation of transgressions, and the wanderings of the poles, stand in one great causal connection with one another. That is shown by their common increase in certain periods of the earth’s history. Only in one case, that of the continental displacements, can we point out, in addition to internal, also external cosmical causes. On that account it is probable that we have to consider the latter as the primum movens, the ultimate cause of all these alterations. But then the relations seem to become complicated. I can, it is true, believe the polar wanderings to be direct consequences of the continental displacements, in spite of Schweydar’s objection that such a displacement only means an exchange of position of equal masses. For the continental block, on account of the higher position of its centres of gravity, has a greater axial distance, and therefore also greater moment of rotation than the sima, whose place it takes; so that in my opinion the axis of inertia of the earth must be influenced by the displacements of the continents. But we have seen that the polar wanderings can now in turn produce continental displacements of another sort. These also will react again on the position of the poles. Thus complicated alternating relations result, the total effect of which can to-day no longer be neglected.