A theoretical model is advanced for the maximum slope angle (angle of initial yield) on the supposition that the average properties of haphazard arrangements of spheroidal particles can be statistically represented by a combination of two different regular packings in a proportion to give the original concentration. The tangent of the yield angle is found to be linearly proportional to the spheroid concentration, which in turn depends upon the axial ratio. The degree and kind of dimensional ordering of the particles can at will be made dependent upon or independent of the concentration. The equations differ slightly, and only in their constants, according to the choice of ordering. Because of the decisive influence of shape inequalities, and the lesser influence of ordering, it appears inadmissible to apply to natural sedimentary particles of ellipsoidal form a model of yield angle based on the sphere. The equations are therefore relevant to the problems of the slope angles assumed by screes and talus and the slip faces of ripples and dunes.

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