Geologic des Meeresbodens

Abstract

THE geology of the sea-floor is geology in the making, since the most important and significant sedimentary rocks were laid down in the sea. The study of these deposits received a great impulse on the discovery by the Challenger Expedition of the unexpected contrast between the marginal and deep-sea formations; and the monograph by Murray and Renard on the deep-sea deposits ranks as one of the most epoch-making of the Challenger reports. Since its appearance the literature on the subject has been voluminous and is unusually scattered, for the processes of marine sedimentation involve large parts of oceanography, physical geography, and geology, and, in addition to the literature of those sciences, essential data are contained in he serials of applied science and in fugitive newspaper reports. The g-eology of modern marine deposits has now been resurveyed by Prof. Andree in a summary of current knowledge of the subject, which this volume completes by a detailed description of marine deposits and by a short account of their economic products. The work is the more convenient for reference as it follows the ordinarily accepted lines of treatment. The first sections deal with marine sedimentation, including the study of wave action and shore deposits, coastal transport, and the mineralogical and oreanic structure of shore sands, mud, coral reefs, and serpula-atolls. The salt beds thrown down by the evaporation of sea-water are grouped as the Halmyrogene products, adopting Krummel's term. In this section of the book Prof. Andree discusses, among other problems, those of coral reefs; and he maintains that recent investigations and the borings at Funafuti have brilliantly and firmly established Darwin's theory of the origin of coral islands. Passing to the coastal shelf, he describes its deposits, and summarises modern evidence as to the depth of current action; he accepts it, on the evidence of the exposure of hard rocks, which he explains as swept clear of mud, at depths of more than 5000 ft. Such bare rock surfaces, however, have also been explained as due to recent subsidence or submarine eruptions, and are not alone conclusive evidence of deep-sea currents. The wide distribution of land material at sea by the wind is illustrated by a map of the tropical Atlantic showing' the areas reached by African dust. Geologic des Meeresbodens. By Prof. K. Andree. Band ii.: Die Bodenbeschaffenheit und nutzbare Materialien am Meeresboden. Pp. xx+689+7 Tafeln. (Leipzig: Gebruder Borntraeger, 1920.) 92 marks.