Seriation, Superposition, and Interdigitation: A History of Americanist Graphic Depictions of Culture Change

Abstract

Histories of Americanist archaeology regularly confuse frequency seriation with a technique for measuring the passage of time based on superposition—percentage stratigraphy—and fail to mention interdigitation as an important component of some percentage-stratigraphic studies. Frequency seriation involves the arrangement of collections so that each artifact type displays a unimodal frequency distribution, but the direction of time's flow must be determined from independent evidence. Percentage stratigraphy plots the fluctuating frequencies of types, but the order of collections is based on their superposition, which in turn illustrates the direction of time's flow. Interdigitation involves the integration of sets of percentage-stratigraphy data from different horizontal proveniences under the rules that (1) the order of superposed collections cannot be reversed and (2) each type must display a unimodal frequency distribution. Ceramic stratigraphy is similar to occurrence seriation, as both focus on the presence-absence of types with limited temporal distributions—index fossils—but the former uses the superposed positions of types to indicate the direction of time"s flow, whereas occurrence seriation does not.