Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/203

Rh separated, as South America and Africa, have the parallelism far better preserved in their coast-lines than in the border-line between the continental slope and the deep-sea floor.

It is not inconceivable that the vulcanicity occurs so frequently near the coasts, because the inclusions of sima of the block are pressed out by the field of stress described above. This explanation is more especially possible in the case of oceanic islands which are surrounded in a circular manner by this field of stress.

A special kind of force must occur on the margin of the plastic continental blocks when these are loaded by a covering of land-ice. If one loads a plastic cake, it will, in its effort to reduce its thickness and extend horizontally, become affected by marginal cracks. This is the explanation of the formation of fiords, which exist in astonishing uniformity on all formerly glaciated coasts (Scandinavia, Greenland, Labrador, the Pacific coast of North America north of 48° and of South America south of 42°, as well as the South Island of New Zealand), and have been already traced back by Gregory, in an extensive yet much too little valued examination of them, to the formation of faults. On the basis of my own observations in Greenland and Norway, I believe that the explanation of fiords as erosion valleys is incorrect, though it is still much advocated at the present day.

By a great number of soundings on the Atlantic continental margins, attention is drawn to a peculiar phenomenon which appears to indicate the submarine continuation of river valleys. Thus the valley of the St. Lawrence is prolonged into the shelf in front down to the deep sea; similarly that of the Hudson may