This volume covers Leg 34 of the cruises of the Drilling Vessel Glomar Challenger. Leg 34 was the first of two "basement" legs of the Deep Sea Drilling Project, in which a primary objective was deep drilling into oceanic basement. This objective was subordinate in previous legs, so that it was necessary to test and perfect the systems that are needed for deep penetration, especially reentry capabilities. A second objective was the investigation of the sediments of the Nazca plate, notable for its concentration of metalliferous sediments in the Bauer Deep. More specifically, the scientific goals were to determine the following: 1) Composition and structure of layer 2A including the prevalence of pillow lavas versus fractured flows, thickness of individual flow units, and changes in composition and physical properties with depth and age. 2) Evidence for off-ridge volcanism and, if present, the difference between off-ridge and ridge volcanism. 3) Interaction between layer 2 and seawater in terms of seawater chemistry, weathering of basalts, and thickness of the weathered zone as a function of crustal age and thickness of overburden. 4) Magnetic properties of ocean-floor basalt as a clue to the nature of magnetic reversals and magnetic properties of sediments as a measure of plate motion. 5) Metalliferous sediments and their distribution as a function of time, sedimentation rate, and proximity to the rise crest. 6) Geologic history of the Nazca plate: abandonment of a "fossil rise" (Galapagos Rise) as a spreading center, and influence of the South American continent on Nazca plate sediments in terms of terrigenous and volcanic deposits and history of the Humboldt Current. Glomar Challenger departed Papeete, Tahiti, on 20 December 1973. After 16 days of steaming eastward, the first site (319) was reached in the Bauer Deep. Further eastward steaming took us to the final two sites (320 and 321) situated near the eastern edge of the Nazca plate just over 350 km from the coast of Peru. The cruise ended in Callao, Peru, on 2 February 1974.