804 



NAFE AND DRAKE 



[CHAP. 29 



Measurements have been taken from Birch, Schairer and Spicer (1942), Hamil- 

 ton et al. (1956), Shumway (1960), Sutton et al. (1957), Kershaw {in litt.) and 

 others. The range of porosity vahies is to 0.25 for hmestones, to 0.4 for 

 sandstones and to 0.5 for shales. Clays, sands and gravels cover the middle 

 range from (/) = 0.2 to 0.6. Ocean sediments range from = 0.4 nearly to 0.9. 

 Deviations from the straight line drawn on the figure are greatest in the case of 

 limestones and dolomites. Of all the points plotted, two-thirds lie almost 

 on the line and the remaining one-third lies above the line. A few large devi- 

 ations occur in the middle range of porosities for clays and gravels but even 

 most of these lie close to the mean line. 



E 



0» (O 



0.2 0.4 0.6 

 Porosity 



0.8 



Fig. 2. Porosity-density data for sediments and sedimentary rocks. Measurements on 

 ocean sediments range from porosities of about 0.40 to 0.85. 



B. Compressional Velocity- Porosity 



Observed compressional velocities are plotted against porosity in Figs. 1 and 

 3. It is apparent that they fall into three groups: the sedimentary rocks at high 

 velocity, the ocean sediments at low velocity, and artificially compacted 

 sediments intermediate between the others. The apparent separation into 

 groups is probably a consequence of easy accessibility of samples in the high- 

 and low- velocity ranges. Wells are cased at the top; coring devices have limited 

 penetration. In Fig. 1 observations are compared with the Wood equation, the 

 time average equation, and with a representative of a one-parameter family of 

 equations proposed by Nafe and Drake (1957). Plotted points for ocean sedi- 

 ments have been obtained from Sutton (1957), Hamilton (1956), Shumway 

 (1960), Laughton (1957) and Kershaw {in litt.) and those for sedimentary rocks 



