﻿190 DR. H. C. SORBT ON THE APPLICATION OF [^^^V I908, 



they subside and afterwards become more or less consolidated. Sand 

 subsides quickly, and almost at once attains a state of comparative 

 stability. On the contrary, in the case of very finely-divided clay 

 and chalk, although they may not take long to subside and leave the 

 water almost clear, yet the accumulated deposit, after settling for 

 a day, acts like an imperfect liquid, and contains no less than 

 86'5 per cent, of water in the case of clay, and 74*3 per cent, in that of 

 chalk, so that the particles must be comparatively far from touching 

 one another. With such fine-grained material an extremely- thin 

 layer of water would suffice. Thus, for particles j^^ inch in 

 diameter, a film ^^-^ inch thick would explain what occurs when 

 no pressure is present, squeezed out thinner when under pressure. 

 On keeping, the material slowly settled ; but, even after a week, 

 the amount of included water was stiU 79-8 percent, in clay, and 

 68' 1 per cent, in chalk. After no further contraction in volume 

 occurred, the amount of included water was 75-5 per cent, in clay, 

 and 64'6 per cent, in chalk. In one case, pipe-clay which had been 

 kept for about a month until no further subsidence was visible, 

 was kept for a whole year without further contraction, and was 

 found still to contain about 75 per cent, of water. In the case of some 

 fine-grained mud from a depth of 2500 fathoms, collected by the 

 Challenger, after it had stood until no further subsidence took place, 

 the amount of included water was no less than 89 per cent. This 

 permanent state is reached most probably when the downward 

 pressure of the particles is equal to the cohesion of the surface-film 

 of water. Hence, we maj' conclude that, since this pressure would 

 increase with the thickness of the deposit lying above, the amount 

 of included water would decrease as the depth became greater, a 

 conclusion which agrees well with observed facts. 



When actually dried, alter having subsided as much as they 

 would, both clay and chalk gave evidence of considerable con- 

 traction, and the volume of included air was in clay 37'9 per cent, 

 and in chalk 41'4 per cent. On water being again added without 

 disturbing the material, this swelled up considerably, as though the 

 water forced itself in energetically, and the final volume of water 

 was in the clay increased to 62-9 per cent., and in the chalk to 57'2 

 per cent. It was extremely interesting to observe the diff'erence in 

 the two materials, for the clay easily broke up into laminae in the 

 plane of subsidence, but the chalk did not. The great contraction 

 in thickness had developed a sort of imperfect cleavage in the clay, 

 but not in the chalk — most likely because the clay contains many 

 flat particles, and the chalk few. 



The Deposition, etc. of Fine-Grained Material. 



Possibly many may think that the deposition and consolidation 

 of fine-grained mud must be a very simple matter, and the results 

 of little interest. However, when carefully studied experimentally, 

 it is soon found to be so complex a question, and the results 



