SECT. 1] THE UNCONSOLIDATED SEDIMENTS 83 



Reference is suggested to this paper and to Chapter 29 for an analysis of 

 the relationships between compressional- and shear- wave velocities, porosity, 

 density and other physical properties. The evidence they presented for dif- 

 ferences between the velocity-depth dependence in deep and shallow water 

 was statistical and based on tabulations of reported velocities and depths. For 

 accurate information on the depth variation of velocity in the uppermost 

 portion of the sedimentary column more sensitive methods are required. 

 Seismic records obtained by shooting and recording on the ocean bottom 

 should provide the necessary additional precision. 



Thicknesses of low- velocity sediments measured by reflection and refraction 

 techniques range from an average of 1 km in the Atlantic to | km in the 

 Pacific. As suggested by Hamilton (1959) in a comprehensive review of compac- 

 tion and lithification processes and of measured velocities and thicknesses, 

 there is good reason to believe that the underlying "Layer 2", described by 

 Raitt in Chapter 6, is also sedimentary material, presumably well consolidated 

 or lithified. This interpretation has been cited by Hamilton and others to 

 establish agreement between the amount of material estimated to have been 

 eroded from continents and that found by seismic measurements in the oceans. 



Lamont Geological Observatory (Columbia University), Palisades, New York. 

 Contribution no. 593. 



References 



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