Sedimentary deposition in the Pacific Ocean is largely influenced by: (1) the great size of the ocean and the relatively small influx of river water; (2) high seismic and volcanic activity, especially in the marginal zone; (3) deep water characterized by relatively high alkalinity and high concentrations of silicate and phosphates; (4) well-developed equatorial current system resulting in high plankton production near the equator in the East Pacific; (5) trenches and other barriers around the margins partially protecting the central regions from influx of coarse continental materials.The area covered by red clay is both relatively and absolutely larger than in the other oceans, mainly because of the greath depths of the North Pacific Basin. Calcareous oozes are particularly extensive in the South Pacific but occur generally at lesser depths than in the Atlantic. Characteristic of the Pacific are large areas of siliceous oozes. Radiolarian ooze borders the northern fringe of the equatorial calcareous zone that underlies waters of high organic productivity. Diatom ooze forms bands in the northern Pacific and in the Antarctic Ocean.Chemical analyses indicate differences in the composition of some older and younger clays. The former are richer in Mn, Fe, and P relative to Ni, Ti, and Al respectively. The well-known high radioactivity of the recent pelagic clays is associated with the authigenic zeolite, phillipsite. A little quartz silt is ubiquitous. The iron-titanium and manganese-nickel ratios appear to be indicative of the proportion of hydrogenous matter. High barium and biogenous copper may indicate rapid accumulation and dissolution of organic remains.Deposits possibly laid down by slumping and turbidity currents occur under the flat bottom in large areas off the northwest coast of North America, and small “sediment lakes” are found at the bottoms of trenches. Direct evidence, such as graded bedding and mixtures of Quaternary and Tertiary fossils, has been found close to topographic highs in the basins of the Mid-Pacific Mountains, north of Alexa Bank, and between the Marquesas and the Tuamotus.In most topographic lows the slow deposition appears to be continuous and uniform. Much of the bottom of the Pacific is irregular; even on slight topographic highs, erosion, nondeposition, or greatly reduced deposition is evidenced. Outcrops of Tertiary calcareous oozes have been found on such highs. Unconformities are evident in some cores. Tertiary calcareous oozes occur at depths and in areas where clay is being deposited around them.Seismic-refraction and reflection profiles suggest sediment thickness of approximately 200 meters in the clay areas and 400 meters beneath the equatorial calcareous oozes. A radiocarbon measurement indicates for the last 14,000 years an average rate of deposition of 3 cm/1000 years in the area of maximum carbonate accumulation below the equatorial divergence. The corresponding rate of deposition of the nonbiogenous components would be about 0.26 cm/1000 years.