10 R. T. CHAMBERLIN AND W. Z. MILLER 
The result of Cadell’s experimentation was to produce a concrete 
picture of the manner in which the complex structure of the North- 
west Highlands may have developed. As pressure was gradually 
applied, the artificially prepared strata were first sliced into separate 
blocks by ordinary reverse slice faults which dipped in the direction 
from which the pressure was applied. A piling up of the sliced 
blocks followed. After sufficient piling up had occurred, a low-angle 
major thrust plane broke through the piled-up mass of slices, 
and the whole overlying mass rode forward bodily upon this 
gently inclined plane which Cadell termed the ‘‘sole” (Fig. 3). 
This behavior would seem to suggest that the heaping up of material 
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Fic. 3.—Major thrust plane, or ‘‘sole,” cutting across minor slice faults. After 
Cadell. 
is an important factor in determining the subsequent break along 
the low-angled “sole.” 
A pressure box patterned somewhat after that of Cadell was 
employed by Willis in his experiments upon Appalachian structure.’ 
But in these interesting and well-known experimental researches 
folding rather than faulting was the prime object of the investi- 
gation. To obtain the desired results Willis used somewhat softer 
materials than those employed by Cadell, and heavily weighted the 
strata with a thick covering of shot to prevent too ready yielding. 
The hardest layers, in most cases, were composed of equal parts of 
plaster and wax, while the less competent beds were still further 
softened by the addition of turpentine, and often by leaving out 
plaster altogether. Fracturing occurred only very incidentally. 
Further researches by Paulcke were directed toward reproducing 
experimentally the folds of the Jura, and the marvelous overfolded 
t Bailey Willis, U. S. Geol. Surv., 13th Ann. Rept., Part II (1893), Pl. LXVI, 
opposite p. 258. 
