The variations in weight percent of the grain size fraction greater than 250 jj. in nine cores from the North Pacific were determined using sampling intervals of 5 to 20 cm. Material in this size fraction is interpreted as transported by icebergs, and fluctuations are attributed to the waxing and waning of glaciers on the surrounding continents. At least eleven periods of increased ice rafting are detected in the cores during the time from 1.2 m.y. ago to the present, whereas only about four are identified from 1.2 m.y. to 2.5 m.y. B.P. The dating and time correlations are based on the magnetic stratigraphy, ash falls, and faunal extinctions. The ice-rafted detritus indicates a cooling beginning about 1.2 m.y. ago and becoming very intense between the Jaramillo event and the Brunhes-Matuyama boundary. This time may correspond to the initiation of mid-latitude glaciations of Europe and North America. At least six zones of ice-rafted sediment are present in the Brunhes normal polarity series. The correlations between these and the carbonate fluctuations of the central Pacific are good. Evidence for a marked interglacial ranging from about 460,000 to 530,000 yrs B.P. occurs within these cores. This interglacial may be worldwide in extent.

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The data from 48 seismic refraction profiles in the western Caribbean Sea and in the Gulf of Mexico are presented in the form of structure sections crossing the Colombian basin, Nicaraguan rise, Cayman trough, Cayman ridge, Beata ridge, Yucatan basin, Campeche bank, and Sigsbee deep. The Cayman trough has a remarkably thin crust, which suggests that it is a tensional feature. Although parts of the basins have a relatively thin crust, similar to the oceanic type, the shallower areas are intermediate or almost continental in structure. In the Gulf of Mexico the main basin is similar to typical ocean basins in structure except that the high‐velocity crust is overlain by very thick sediments. The depth to the mantle is appreciably greater in the Gulf than in an ocean basin. This may be partly the result of loading by the sediments, but large scale tectonic activity is a more likely cause. The Sigsbee escarpment, the northern boundary of the main basin, appears to be the surface expression of a fault or sharp flexure in the layers beneath the unconsolidated sediments.

By the use of suitable chemical and radiometric techniques the natural radiocarbon concentration in the dissolved bicarbonate of 135 samples representing the major water masses of the Atlantic Ocean has been determined with a precision ranging from 0.5 to 1.3 per cent. Whereas the results from a given water mass exhibit a standard deviation only slightly exceeding that predicted from the experimental error alone, measurable differences exist between the major water masses, the total range in C14/C12 ratio being about 10 per cent. Corrections for the bomb‐produced C14 effect and the industrial CO2 effect have been applied where necessary. The surface water C14/C12 ratios show a progressive increase from south to north, ranging from 120 per mil lower than the preindustrial atmospheric value in the Antarctic to 50 per mil lower in the North Atlantic. Deep water masses originating in the high latitudes of the southern hemisphere have consistently lower C14/C12 ratios than those originating in the high latitudes of the northern hemisphere. A layer of water of high C14/C12 ratio found at depths between 1200 and 2400 meters in the western North Atlantic may well represent a wedge of young water penetrating the older North Atlantic deep water. Bottom water in the eastern basin of the North Atlantic has a 20 per mil lower C14/C12 ratio than the corresponding water in the western basin. According to a steady‐state circulation model, most of the water below 600 meters in the North Atlantic remains at depth for an average of 650 years. Corresponding residence times for water masses of Antarctic origin are less than 350 years. A circulation model explaining the prominent features of the C14 distributions in the atmosphere‐ocean system is based on a south to north transport of water along the surface of the Atlantic Ocean, with a return flow at depth. The Atlantic and Pacific communicate through the Antarctic. On the basis of this model, despite the lower ΔC14 values, the mean residence times of water in the deep reservoirs of the Pacific may not exceed those for the deep Atlantic by more than 30 per cent. Although results of C14 analyses on tree rings suggest that the oceans are reasonably close to steady state, the possibility of nonsteady‐state circulation must be considered. It is shown that the present C14 distribution in the oceans could be achieved through the storage of C14 in the atmosphere and surface oceans during a relatively short period of greatly restricted bottom water formation. If nonequilibrium effects are important the residence times computed from the steady‐state model could be considerably in error.