oil-exploration and civil -engineering literature because of 

 industrial interests. 



Unfortunately, when the physicist studying the results 

 of underwater sound experiments requires knowledge of the 

 physical properties of the sea floor for any given area, he 

 usually finds that the geologist or geophysicist can only 

 postulate approximate models with limits to the ranges of 

 the more common physical properties, and does not have 

 measurements and related theoretical work to report for 

 his use. The ultimate result of the work presently in 

 progress at several institutions will allow prediction 

 (within reasonable limits) of various properties of the sea 

 floor. A recent general summary of sediment distributions, 

 and ranges of some of the more common physical prop- 

 erties, are indicated in tables 1 and 2 (compiled at the 

 request of a committee of the American Geological Institute). 

 These tables are of interest in defining limiting values of 

 the physical properties noted. 



One of the problems in measuring the acoustic prop- 

 erties of sediments in the laboratory is to expel, or keep 

 out, gas or air, especially if an artificial sediment is used 

 in the experiments. If natural sediments are used, and 

 they contain organic matter, the measurements must be 

 made immediately, before gas is generated. If the in situ 

 sediments contain gas, as they do in many bay, estuary, or 

 near-shore environments, then valid measurements can 

 probably be made only in situ . A plot of sound speed 

 versus percentage of water saturation indicates immediately 

 whether there has been experimental difficulty with gas or 

 air. If the sound speeds at 100 percent saturation are sig- 

 nificantly less than about 1500 m/sec for sand, for example, 

 almost certainly there has been difficulty with air or gas 

 within the pores of the sediment structure. It should be 

 noted, however, that many such studies (especially in civil 

 engineering) are intended to show the effects of partial 

 saturation and their validity in this respect is not questioned. 



Because of the various difficulties of getting a really 

 good, relatively undisturbed sample back to the laboratory, 



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