Many of the problems of past geological history and of present processes of sedimentation require a knowledge of the rate of accumulation of marine sediments. A very important step in the determination of the rate of deposition of a sediment is the measurement of a time interval. This is equally true whether use be made of the stratigraphic method with core samples or the supply method based upon the rate of supply of sedimentary material to the sea. The stratigraphic method gives rates for individual localities, whereas the supply method yields averages for large areas over long periods of geological history.