It was mentioned previously that Hathaway (report in preparation) demonstrated 

 that the quantity of micro-organism skeletons was directly related to the water content 

 in selected Area C samples. It is likely that this relation also is valid in other areas 

 subject to pelagic deposition. Both skeletons of micro-organisms and platy clay 

 minerals are characterized by very large surface areas; the former, however, probably 

 contribute relatively little cohesion or plasticity to a sediment, while the latter has 

 an opposite effect. An abundance of skeletal remains in fine-grained sediments influ- 

 ences the structural properties, in addition to the relation of increased interstitial 

 water content to reduced cohesion. It appears reasonable to suppose that parallel 

 rearrangement of cardhouse structure following disturbance will be inhibited by an 

 abundance of microskeletal remains. Consequently, it also is likely that sensitivity 

 will tend to be inversely related to the quantity of microskeletons. 



Thixotrophy is defined by the ASCE as the property of a material that enables it 

 to stiffen in a relatively short time on standing, but upon agitation or manipulation 

 to change to a very soft consistency or toa fluid of high viscosity, the process being 

 completely reversible. Van der Waals forces and Coulombic forces are the principal 

 interparticle forces affecting clay particles. Van der Waals forces normally cause 

 attraction, but decrease with about the sixth power of the distance from the particles; 

 Coulombic forces, decreasing with the square of the distance, are the electrostatic 

 attraction between the positively charged edges and negatively charged faces of 

 different particles and also the electrostatic repulsion between two edges or two faces 

 of adjacent particles (Hvorslev, 1961, p. 170-171). A detailed discussion of these 

 forces and their relation to cohesion is given by Lambe (1961). According to a recent 

 hypothesis (Mitchell, I960, p. 29-31), externally applied shearing energy in remold- 

 ing causes the platy clay particles (previously in cardhouse structure) to be rearranged 

 in a parallel structure leaving adsorbed water layers and ions in a high energy structure 

 where the attractive forces are much greater than repulsive forces immediately after 

 shearing stops. With time, thlxotropic hardening produces structural rearrangement to 

 a lower energy condition, and the attractive forces decrease. A new equilibrium 

 results when water returns to a low energy structure, attractive and repulsive forces 

 are equal, and clay minerals once again have a more or less cardhouse structure. 

 Thixotropic strength regain may be inversely related to the abundance of microskeletons 

 in clayey skeletons, because a large quantity of skeletal material will inhibit electro- 

 chemical forces tending to produce rearrangement of the clay minerals. 



As stated in Appendix A, it is uncertain whether or not the salt content of pore 

 water in the surface few meters of submarine sediments generally is constant or variable. 

 Should the salt contents prove to be variable, and particularly if it should be inversely 

 related to depth, investigations of salt leaching from marine clays reported by Rosenqvist 

 (1946-published in English, 1953; 1955), Skempton and Northey (1952), Bjerrum (1954b), 

 and Bjerrum and Rosenqvist (1956) may prove highly applicable to marine geological 



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