On Leg 3, 10 sites were investigated in the South Atlantic Ocean, mainly on the Mid-Atlantic Ridge. Drilling at each site was deep enough to reach the basalt basement. On Leg 4, nine sites were drilled in the western South Atlantic and Caribbean region. The objectives were to enhance knowledge of basins adjacent to continental margins, sea-floor spreading, nature of the transverse fractures of the Mid-Atlantic Ridge, geology of island arcs and trenches, and to explore the geologic history of the Caribbean. Cores described include those from two sites off the Lesser Antilles, and three in the Caribbean, in the central Venezuela Basin.