The clay mineral composition of Recent sediments from the modern Mississippi River Delta and offshore regions in the vicinity of the Delta is reported. Montmorillonite is the dominant clay mineral being deposited in the Delta region. A small amount of this component changes to illite and chlorite. It is suggested that this material represents degraded micaceous material undergoing regradation, and thus represents the approximate contribution of the Ohio River drainage system to clay mineral assemblage. The bulk of the montmorillonite, presumably bentonitic in character, undergoes no apparent diagenesis. It is suggested that this material represents the approximate contribution of the drainage basin of the Missouri River system.