Grain size analyzers provide the size frequency spectrum in terms of grain number, or the weight or volume percent within specified size intervals. If the sample is comprised of sedimentary particles, the distribution can range from well-sorted (i.e., having a narrow size range) to poorly sorted and polymodal. The distribution may be numerically represented, such as with statistical indices (Friedman, 1962; Folk, 1966; Doeglas, 1968; Davis, 1970; Buller & McManus, 1972; Roy & Biswas, 1975; McLaren, 1981), modal frequencies (Clark, 1976; Syvitski & Macdonald, 1982), or graphs (Passega, 1964; Pejrup, 1988), such as a plot of relative frequency and particle size (Burger, 1976). Size frequency distributions can be discussed on their own merits (Visher, 1969) or within larger matrices containing size information on other samples (Glaister & Nelson, 1974).

The four chapters that comprise Part IV deal with the science of grain size data interpretation and manipulation. Chapter 16 reviews how statistical parameters of particle size can describe a sedimentary environment. The author suggests that this information should come from the average of many samples of the parent population, rather than from a single sample (Hails & Hoyt, 1969). When plotted against each other, these new parameters are capable of separating the samples into the appropriate sedimentary environments. Such diagrams show aspects relating to the physics of sediment transport that may allow for a more refined paleogeographic interpretation.

There has been a long-standing debate on the form of the natural probability distribution that sedimentary samples reflect, in terms of their size spectra (cf. Middleton, 1962).