58 HISTORY OF THE OCEANS 



consolidation curves intermediate between clay and sand, but 

 always on the high porosity side of clay at the same pressure 

 (Fig. 3)._ 



The difference between the porosity of a calcareous ooze and a 

 clay at the same pressure and depth is quite distinctive: the clay 

 porosity is always less than that of the ooze. Glohigerina ooze is 

 largely composed of shells, or tests, of planktonic Foraminifera; 

 mechanical analyses of typical calcareous oozes (Revelle, 1944, 

 pp. 144-147) show that the size distribution of particles is such 

 that most calcareous oozes can be considered as very specialized 

 types of sandy silt or sand-silt-clay. It should not be surprising, 

 therefore, if the behavior of Globigerhia ooze, or calcareous ooze, 

 under gravitational pressure follows the consolidation cur\'es ex- 

 pected for sandy silt or silty sands. In addition, calcareous ooze 

 is a specialized sandy silt in that many of the grains are hollow 

 shells of calcium carbonate; these delicate shells after crowding 

 together under compaction will crush much more easily than typi- 

 cal shallow water sandy silt grains. It should be expected, then, 

 that calcareous ooze will show a faster decrease in porosity than 

 typical quartz particle sediments. Figure 3 illustrates this for the 

 ooze which Laughton compacted. This should also be true of other 

 similar oozes of high calcareous shell content. 



How close do the laboratory determinations come to the actual 

 consolidation in the field ; both as to settlement under buildings 

 or under gravitational consolidation due to the weight of the sedi- 

 ment itself? This matter has been extensively studied, and it is 

 known that the laboratory results allow close prediction of the 

 actual consolidations (Skempton, 1953; Schmertmann, 1955). 

 Usually the laboratory-derived void ratios are slightly less than 

 those in the field at a given pressure; this is thought to be due to 

 loss of strength because of disturbance during sampling. 



The intergranular pressure (owing to the weight of sediment 

 grains) which is used in computations of consolidation is inde- 

 pendent of the depth of the water as long as free movement of the 

 water can take place, so that the excess porewater pressure can 

 become zero. The question of hydrostatic uplift (or buoyancy of 

 mineral particles due to Archimedes' principle) is important in 



