The Origin of Continents and Oceans

Abstract

THE wide appeal of Prof. Wegener's theory of the arrangement of ocean and continent is shown by, the issue of a third greatly revised edition and of this excellent English translation. His theory is that the continents consist of rigid blocks of sial, or rock charac terised by a high percentage of silica and alumina, which are floating partly submerged in a sheet of sima, Ojrrock material composed mainly of silica and magnesia; that the existing continents are due to the breaking up of a once continuous sheet of sial, the fragments of which have drifted to their present positions in con sequence of the earth's rotation; and that this drift occurs owing to the plasticity of the sima. Prof. W;egener believes that the continents have been moved for great distances even in geologically recent times, and he thereby, with great ingenuity and attractive ness, explains many problems of geography, geology, climatology, biology, and geodetics. The process offers an easy escape from difficulties and is not to be dis missed as impossible or scouted as fantastic; for in all probability sima is more plastic than sial, and the natation of the world must make the continental masses tend to lag westward, and press centrifugally toward the equator. The view that the continental masses are subject to some horizontal drift has been often adopted, as, for example, by the reviewer in 1915 (Scot. Geog. Mag., 31, pp. 258–60) to explain the folded nature of the Pacific margin of America, in contrast to the coastal structure on both sides of the Atlantic, and the prevalence of fiords on western coasts. There is no a priori objection to the principle, and the verdict on Prof. Wegener's theory will depend on whether it explains more difficulties than it creates. The Origin of Continents and Oceans. By Prof. Alfred Wegener. Translated from the third German edition by J. G. A. Skerl. Pp. xx + 212. (London: Methuen and Co., Ltd., 1924.) 10s. 6d. net.