Figure F4. A. Textural classification scheme for siliciclastics, modified from Shepard (1954) by subdivision of the central triangular field into sandy clay, silty clay, sandy silt, clayey silt, clayey sand, and silty sand. The sand-, silt-, and clay-sized fractions are defined using the Wentworth (1922) grade scale. B. Procedure for naming mixtures of biogenic and siliciclastic sediments. In this scheme, the names shown for microfossil components and the siliciclastic fraction are examples only (i.e., placeholders) and can be replaced by any valid textural (for siliciclastic fraction) or microfossil name.