Cortex Ratio Analysis

Cortex ratio analysis is a quantitative method for assessing whether a lithic assemblage represents the complete reduction of the stone present, or whether pieces have been carried into or out of the deposit. Its insight is that every stone nodule begins entirely covered by a weathered outer rind, or cortex, and that knapping progressively removes this cortex as flakes are struck; a complete, undisturbed reduction event should therefore retain a predictable amount of cortical surface relative to the volume of stone it contains. By measuring the cortical surface area actually observed across all artifacts and dividing it by the cortical surface area expected from the assemblage's total volume, Douglass and colleagues derived a single index — the cortex ratio — that diagnoses assemblage completeness. A ratio near one indicates an intact assemblage, less than one indicates that cortical pieces were removed, and more than one indicates that cortical material was imported. Building on the macroscopic measurement conventions Andrefsky systematizes, the method turns cortex from a qualitative stage indicator into a rigorous test of artifact transport and site formation.