Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/104

78 America consisted to a great extent in a rotation. A similar state of affairs applies to the connection of the blocks at the Bering Straits. Diener’s objection, already mentioned, “Whosoever pushes North America on to Europe breaks its connection at the Bering Straits with the Asiatic continental block,” is only met with in a Mercator’s map, but not on a globe, for the movement of North America consists essentially of rotation. At this point the blocks were never torn away from each other, and the bridge lay above water in the Silurian and Devonian, again in the Middle Carboniferous to the Middle Permian, then in the Lias and Middle Jurassic (Dogger), and finally from the Cretaceous to the Quaternary, when it was probably partially obstructed by the ice.

Let us now proceed to a discussion of the Atlantic rift from the biological point of view. The Atlantic is generally considered to be young in comparison to the Pacific. Ubisch writes: “In the Pacific Ocean we find numerous ancient forms, as Nautilus, Trigonia, ear-seals. These forms are absent in the Atlantic Ocean.” W. Michaelsen drew my attention to the fact that the present distribution of earth-worms offers particularly unobjectionable evidence of the former Atlantic land connection, because usually the sea is an insurmountable obstacle to these animals. A