Sand fractions in sediment samples from the Atlantic Continental Shelf will be analyzed for grain-size distribution with an improved sedimentation tube. The instrument measures size by means of apressure differential between two columns of water having a common head. Pressure rises abruptly when sand is added, and decreases as particles of different sizes settle. Pressure variation recorded on a moving chart constitutes a cumulative frequency graph of the grain-size distribution.. A wide range of sizes in a sediment causes grains of most size classes to settle more rapidly than predicted by Stokes Law. Calibration of the instrumment results in a settling curve that is parallel to but displaced to the left of the Stokes Law ccurve over a time base.