The British submarine gravity surveys of 1938 and 1946

Abstract

The structure of the ocean basins is one of the most outstanding problems of geology. The fact that the rocks which form the floor of the ocean are not directly accessible for investigation renders its solution a matter of considerable difficulty. Until recently, almost the only data available were derived from soundings and bottom samples, but the development of geophysical methods now provides means by which additional information can be obtained. One of the most notable advances was the development, by Professor F. A. Vening Meinesz, of the submarine pendulum apparatus which enables accurate measurements of gravity to be made at sea. More recently, the application of the seismic technique has provided another powerful means of investigation. In 1935, Professor M. Ewing (Ewing, Cary & Rutherford 1937) used this method to study the structure of the continental shelf on the Atlantic seaboard of the United States. His results indicated that although the depth of the water only increased very gradually out to the 100-fathom line, the underlying basement rock, as it may be called, shelved more steeply, and near the edge of the shelf was overlaid by many thousands of feet of less compacted sediments. This work was soon followed by similar investigations carried out by Dr E. C. Bullard (Bullard & Gaskell 1941) at the mouth of the English Channel, where the same type of structure was found. These two regions differ in that the main structural lines in the eastern United States run roughly parallel to the coast, while at the mouth of the English Channel they are more nearly at right angles to the edge of the continental shelf. It appears probable, therefore, that the presence of large thicknesses of sediment may well be a general feature of the edge of the continental shelf.