LOW-ANGLE FAULTING 12 
In preparing this combination it seemed best to mix the plaster and 
clay dry and, when thoroughly mixed, to put the mixture in the 
machine in that state and wet it down with water as the material 
was poured in. The most homogeneous mixtures were developed 
in this manner. 
When the box was filled to the desired depth, the wet mass was 
allowed to set for a period of from three to seven days, until the 
material was not readily dented with a trowel. The length of time 
required depended considerably upon the combination of materials 
used. The greater the proportion of clay the longer the period 
of time necessary for the material to harden. When deemed 
sufficiently hard, the screw was turned and the process of crushing 
begun. The pressure was brought to bear gradually. After a 
single turn of the screw, or only a small fraction of a turn, the side 
of the box was removed and the resulting deformation observed. 
This cautious turning of the screw, with frequent halts to view the 
results, was maintained till the end of each experiment. 
After treating structureless homogeneous materials of a con- 
siderable range of competency, tests were made with bedded homo- 
geneous materials to discover how simple bedding planes, as lines 
of weakness, influenced the angle of faulting. The procedure was 
to place a layer of equal parts of plaster and clay in the machine, 
soak it thoroughly with water, and quickly smooth it with a trowel. 
After a few minutes, when the bed had hardened slightly, another 
layer of the same material was laid upon it and treated in the same 
manner. In this way five or six layers were built up. The whole 
mass was then allowed to set until rigid, and afterward crushed. 
To test the influence of an alternation of beds of different 
competency upon the angle of faulting, Cadell’s line of attack 
was followed at the outset. Plaster and sand were used respec- 
tively for the competent and incompetent beds. The sand was 
poured into the machine, bedded down, and then well dampened 
with water. While still wet a layer of pure plaster was added, 
followed as quickly as possible by another layer of sand and 
another of plaster, until four to six layers weré built up. The 
plaster absorbed water at once and became hard, so that a long 
wait before crushing was less necessary than when clay was involved. 
