ABSTRACT

The results of detailed mechanical analyses of shallow marine sediments collected around the coasts of the Cape of Good Hope are presented. The sediments are quartz sands containing 20 to 40 percent shell fragments. Weight percentage cumulatives plotted on arithmetic-probability paper after phitransformation show up to four modes. The cumulatives can in all cases be expressed in terms of lognormal components, and it has been found that the points of inflexion separating the three principal modes persistently occur at about 0.8 and 2 phi. The shapes of the cumulatives and positions of the inflexion points are not obviously related to shell content, analyses of acid leached sands giving the same results (with trivial exception) as their unleached counterparts. Consideration of the signi icance of the 0.8 and 2 phi inflexion points in terms of various factors which could induce polymodality, leads to the conclusion that the Stokes-Impact Formulae account for the 2 phi point and mixing of the suspension and traction loads is responsible for the 0.8 phi point.