Submarine seismic investigations

The refraction seismic method has been used to investigate the form of the surface of the hard rocks underlying the sediments on the continental shelf to the west of the English Channel. This surface is found to slope steadily downwards on receding from the land, and to reach a depth of over 8000 ft. at the 100 fm. line. The velocity of elastic waves in the sediments is about 6000 ft./sec. near the surface and up to 9700 ft./sec. lower down, compared to 16,000—22,000 ft./sec. in the basement. The bearing of these results on the structure and history of the shelf is discussed.