Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/209

Rh Thus, according to our idea, the island festoons, especially those of Eastern Asia, are to be considered as marginal ranges, which, by the westerly drift of the continental masses, become separated from them, because those festoons remain attached to the deeply-solidified ancient floor of the sea. The younger and more mobile ocean floor crops out in a window-like fashion between them and the continental margin.

This is a different theory from that which F. v. Richthofen has put forward, starting, of course, from quite other assumptions. He thought that the festoons originated through a tensile force in the crust of the earth coming from the Pacific. The festoons of islands, together with a broad zone of the neighbouring mainland, also characterized by the curved course of the coast and of the elevations, would form a great system of fractures. The area between the chain of islands and the coast of the mainland would be the first continental step which would be submerged below the surface of the sea on the west, as a consequence of a tilting movement, whilst the eastern margin would project as an island-festoon. Richthofen believed he could recognize two further similar steps on the mainland, the depression of which, however, was less. The regular arc-like form of these fractures certainly raised a difficulty; nevertheless, it was thought that by referring to curved cracks in asphalt and other substances this objection could be invalidated.

Though it must be freely acknowledged that this theory possesses the merit historically of being the first to break consciously with the dogma of a universally effective arching pressure, and to call in tensional forces for the explanation of earth structures,