connection between both continents; moreover, the affinities are confined to such elements as can bear the cold.
Naturally a large number of bridges which to-day are represented by shallow seas are also assumed. The adherents to the doctrine of the bridging-continents have up to the present made no differentiation between the bridges over the oceans and those over the continental shelves. It must be especially emphasized that the displacement theory only deals with the question of land connection over the present-day deep sea areas for which new ideas are developed, whilst for the shelf-bridges, as the Bering Straits between North America and Siberia, the earlier view of submergence and re-emergence of dry land remains absolutely undisputed.[1]
The adherents to the doctrine of the submerged continental bridges have thus a very strong argument: the former existence of broad land connections between continents which are widely separated at the present day can scarcely be doubted on account of the similarity of the fossil faunas and floras and the affinity of the existing ones. That these land-bridges were formed by continents which later sunk to the depths and form the present floor of the ocean, was assumed, on the grounds of the contraction theory, as self-evident and not requiring further proof, since the possibility of
- ↑ Among the numerous misapprehensions on which Diener’s opposition to the new idea is based (“Die Groszformen der Erdoberfläche,” Mitt. d. k.k. geol. Ges. Wien, 58, pp. 320–349, 1915), already for the greater part refuted by Köppen (“Über Isostasie und die Natur der Kontinente,” Geogr. Zeitschr., 25, pp. 39–48, 1919), the following is found:—“Whoever pushes North America towards Europe breaks its connection with the Asiatic continental block at the Bering Straits.” This objection, obvious as it is on a Mercator’s map, vanishes if a globe be taken; the question is essentially one of rotation of North America about Alaska.
