Size frequency distributions of sediments and the normal phi curve

The substitution of a logarithmic variable in the Gaussian function yields a logarithmic probability law (the normal phi curve) which has all the geometrical properties of the conventional normal law. That is, it is bell-shaped and symmetrical about its mean value, and it is completely described by two parameters, the phi mean and the phi standard deviation. Simple analytic and graphic methods are described for testing data for normalcy. Finally, some of the theoretical implications of normal phi curves are given, in terms of environmental factors which may control them.