This volume covers Leg 40 of the cruises of the Drilling Vessel Glomar Challenger. Leg 40 was historically significant as the first expedition of the Deep Sea Drilling Project devoted exclusively to continental margin drilling. The thick sedimentary successions penetrated at all six sites consistently pushed to the limit the technology for single bit penetrations. The leg commenced on 17 December 1974 at Cape Town, South Africa, and terminated 60 days later on 15 February 1975 at Abidjan, Ivory Coast. Three geographic regions were visited in the South Atlantic Ocean, all on the western continental margin of Africa. These regions included: (1) the upper and lower continental rise in the southern Cape Basin; (2) the abutment area of the Walvis Ridge against the continental slope of Namibia (southwest Africa); and (3) the marginal salt plateau of the continental slope of Angola. The primary objectives of the continental margin drilling program in the South Atlantic were to obtain as complete a representative sedimentary sequence as possible from continental slope and rise physiographic settings north and south of the Walvis Ridge morphologic barrier, as well as sediments from the ridge itself.