STRATIGRAPHY OF THE DEEP-SEA FLOOR 



57 



are derived from a large number of field and laboratory deter- 

 minations which are in accord with a large number of plots from 

 other sources collected by the writer, but not shown on the figure 

 to preserve clarity. Laughton (1957) has published results of 

 consolidation-velocity studies on deep-sea materials. Laughton's 

 ^-log p curves (Fig. 2) have been added to the curves of Skempton 

 (1953) and of Terzaghi and Peck (1948). 



Discussion 



The difference in the consolidation behavior of sand and clay 

 has long been known and studied in soil mechanics. Sands, after 

 a quick mechanical rearrangement of particles, will show rela- 

 tively slow decreases of porosity under increasing pressure. The 

 adsorbed water layer, if any, around sand grains is unimportant 

 in this consolidation history. Clay, on the other hand, shows a 

 relatively fast decrease in porosity with increasing pressure and 

 with expulsion of both the porewater and the adsorbed water 

 around the grains. Figure 3 illustrates these differences at pres- 

 sures greater than 50 kg/cm'-. Mixtures of sand and clay will have 



Fig. 3. Consolidation {e - log p) curves for clay and sand. A, soft Detroit clay; 

 B, shale with hydrostatic uplift (porosity data from Skeels, 1950); C, colloidal 

 clay (Skempton, 1953); D, terrigenous mud (Laughton, 1957); E, 80% sand and 

 20% mica; F, dense sand; G, 90% sand and 10% mica; H, loose sand (A and 

 E-H from Terzaghi and Peck, 1948); I, Globigerina ooze (Laughton, 1957). 



