Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/204

178 be followed to a depth of 1450 m. The same is the case on the European side, before the mouth of the Tagus, and specially in the “Fosse de Cap Breton,” 17 km. north of the mouth of the Adour. But the most beautiful phenomenon of this kind is certainly the Congo Channel in the South Atlantic, which may be traced to a depth of 2000 m. According to the customary explanations, these channels are drowned erosion valleys, which had their origin above the water. This, however, appears to me to be extremely improbable, first on account of the great amount of submergence, secondly on account of their general distribution (by a sufficiently large number of soundings they will probably be found on all continental margins), and thirdly because only a certain selection of river mouths show the phenomenon, whilst those lying between them do not. I believe it to be much more probable that we are here also dealing with rifts in the continental margin which have been used by the rivers. In the case of the St. Lawrence, this fissure-nature of its bed is, as a matter of fact, proved geologically. In the case of the “Fosse de Cap Breton,” which forms the innermost end of the deep-sea rift of the Bay of Biscay, with its book-like opening, its very position renders this explanation plausible.

But island festoons form the most interesting phenomenon of the continental margin, and are especially well developed on the east coast of Asia (Fig. 39). If we consider their distribution in the Pacific Ocean, we see a system developed on a large scale. This is especially the case if we conceive of New Zealand as a former festoon of Australia; then the whole west coast of the Pacific Ocean will be covered with island festoons whilst the east coast is