This volume covers Leg 3 of the cruises of the Drilling Vessel Glomar Challenger. On 1 December, 1968, the Glomar Challenger departed Dakar, Senegal, to commence Leg 3 of the Deep Sea Drilling Program. On Leg 3, fifty-five days were spent at sea, during which time the Glomar Challenger travelled 11,000 kilometers to Rio de Janeiro, Brazil. 17 holes were drilled at 10 sites in the equatorial and south Atlantic Ocean between Dakar, Senegal, and Rio de Janeiro, Brazil. The sites are located over three major physiographic features of the sea floor: the Sierra Leone Rise (Site 13), the Mid-Atlantic Ridge (Sites 14 through 20), and the Rio Grande Rise (Sites 21 and 22). The drilling penetrated to basalt (basement) at all Mid-Atlantic Ridge sites, located in profile across the ridge at about 30°S latitude; and, drilling was terminated in sediments at other sites.