THE NAVY OCEAN SCIENCE PROGRAM 33 



layers. It recently has been shown by the potassium-argon 

 method that deposition rates measured in cores of sediment in 

 parts of the North Pacific are millimeters per thousand years. 

 This is comparable to present-day rates. Identification of volcanic 

 ash beds from historical eruptions of volcanoes have established 

 rates as high as one meter per thousand years in the western 

 Mediterranean Sea, an area with a potentially huge supply of 

 detritus. Studies on orospherid radiolarians (siliceous skeletons 

 of spicules) in sediments show that these fossils were laid down 

 rapidly dxiring the Tertiary period, and therefore may be useful 

 in assigning stratigraphic ages to otherwise iinfossiliferous ocean 

 sediments. Other investigations have shown that the oldest 

 sediments in the ocean deeps are more than 100 million years 

 old; the previous oldest identified age was 70 million years. 

 These and other means of dating are being used in an exciting 

 race to establish the major framework of the history of the ocean 

 basins. The seismic-reflection profiler has supplemented these 

 methods by discovering significant outcroppings of layers of 

 sediment or rock that could then be sampled and dated. This 

 program continues very aggressively and is being accompanied 

 more and more by excellent measurements of acoustical prop- 

 erties. 



Studies of sediments being conducted along the continental 

 margins are showing the existence of complex structures on both 

 the shelves and slopes. The studies indicate variations in rate 

 of uplift and subsidence, and sometimes indicate how the con- 

 tinent has grown in the seaward direction. It has been shown 

 that continental rocks affect the shaping of the continental 

 shelves and control the distribution of sediments at sea. Studies 

 are being made on the origin and nature of submarine canyons, 

 particularly on the mechanism producing the erosion (the 

 mechanism has not been completely resolved). These investiga- 

 tions, though obviously valuable, are but a mere beginning. 

 We need to know more of the exact shape, stability, and dynamics 

 of the shelf and sloping regions off our continent, both for sonar 

 and for the installation of structures. 



Seismic-refraction measurements provide the most reliable 

 determinations of thicknesses of crustal layers in the earth, 



