This volume covers Leg 68 of the cruises of the Drilling Vessel Glomar Challenger. The sixty-eighth cruise of Glomar Challenger was devoted to using the newly developed Hydraulic Piston Corer (HPC) to recover undisturbed, continuous sequences of unlithified sediment. We returned to the vicinities of two rotary-drilled sites (83 and 154). The stratigraphy of these sites indicated that uninterrupted sections of late Neogene and Quaternary sediment should exist at these locations. The ship left Curacao, Dutch Antilles, on 13 August 1979, cored for 11 days at Site 502, and transited from the Caribbean through the Panama Canal. Site 503, in the eastern equatorial Pacific was cored for seven days, and we then finally transited to Salinas, Ecuador. The general objectives of this cruise were to use the newly developed HPC to recover two undisturbed, continuous records of the late Neogene and Quaternary, one from the western Caribbean and the other from the eastern equatorial Pacific, and to test the coring capabilities of the HPC. The HPC had been successfully used only once before (Leg 64, Site 480), and it recovered a spectacular section of laminated (or varved) diatomites from the Gulf of California. This initial success inspired strong interest among the paleoceanographic community in using the HPC to continuously core high priority sites that were thought to have continuous records, to be pelagic or at least to contain a high biogenic component, and to be optimally located for answering important paleoceanographic questions. Previous attempts to obtain detailed records at some of these locations were plagued by spot coring, poor recovery, and badly disturbed sediment.