This volume covers Leg 26 of the cruises of the Drilling Vessel Glomar Challenger. Leg 26, the fifth cruise of D/V Glomar Challenger in the Indian Ocean, and the first cruise of Phase III of the Deep Sea Drilling Project, began when the ship sailed from Durban, South Africa, on 6 September 1972 and ended when we docked in Fremantle, Western Australia, 30 October. During the course of Leg 26, Glomar Challenger steamed 5530 miles (9447 km) and drilling operations were carried out at nine sites drilling 12 holes in water depths ranging from 1144 to 5361 meters. The Indian Ocean south of 20°S is considerably less well known than the more northerly part. The sites drilled on Leg 26 were selected to try to elucidate a number of specific problems of both local and broad regional significance, as well as to add to our general knowledge of the area. Briefly, the particular problems selected were: 1) To locate the oldest sediment in the Indian Ocean and thus possibly the date of the initial breakup of Gondwanaland (Sites 250, 256, 257); 2) To determine the effects of the initiation of the Circumpolar Current on southern Indian Ocean sedimentation (Sites 250, 252, 256, 257, 258); 3) To determine the history of spreading of the Southwest Branch of the Indian Ocean Ridge and the history of the crust and oceanic sedimentation in that general region (Sites 250, 251, 252); 4) To further examine the nature and history of the Ninetyeast Ridge (Sites 253, 254); 5) To determine the age, nature, and history of Broken Ridge-Naturaliste Plateau, supposed micro-continents (Sites 255, 258).