This volume covers Leg 78A of the cruises of the Drilling Vessel Glomar Challenger. This volume presents the initial scientific results of Deep Sea Drilling Project Leg 78A, which cored the seaward portions of the Lesser Antilles subduction complex on the eastern edge of the Barbados Ridge. Leg 78A was basically a drilling experiment to penetrate the toe of a particular type of accretionary complex at a convergent margin and reach materials whose eventual fate will either be subduction or underplating of the accretionary pile. The cores obtained document with considerable clarity the structure and style of deformation of the zone of active sediment accretion. A variety of downhole measurements provide important indications of the actual mechanics of faulting and deformation in the area. Leg 78A began and ended in San Juan, Puerto Rico and took place between February and March of 1981.