LOW-ANGLE FAULTING 9 
lands, where the thrust planes cut through very heterogeneous 
assemblages of rock material. Different principles apparently 
control the latter. 
It was with a view to obtaining light upon the mechanism of 
the Scotch overthrusts that Cadell, in 1888, even earlier than Hayes, 
undertook his experimental researches which since have become 
classic. In these instructive researches Cadell made use of a 
pressure box, one side of which could be thrust forward by means 
of a powerful screw. In this box he built up a succession of layers 
of plaster of Paris, interstratified with layers of sand, to imitate 
beds in the earth. After the plaster had set into rigid strata, 
lateral pressure was applied by means of the screw which moved 
the pressure block. In this manner, as the final outcome of many 
trials, he succeeded in imitating rather closely the peculiar imbricate 
and overthrust structure which the members of the Scottish survey 
were deciphering from the greatly disturbed terranes of the North- 
west Highlands.* | 
Those of Cadell’s conclusions which relate to overthrusting may 
be quoted: 
1. Horizontal pressure applied at one point is not propagated far forward 
into a mass of strata. 
2. The compressed mass tends to find relief along a series of gently inclined 
thrust planes, which dip toward the side from which pressure is exerted. 
3. After a certain amount of heaping up along a series of minor thrust 
planes, the heaped-up mass tends to rise and ride forward bodily along major 
thrust planes. 
4. Thrust planes and reversed faults are not necessarily developed from 
split overfolds, but often originate at once on application of horizontal pressure. 
5. A thrust plane below may pass into an anticline above, and never 
reach the surface. 
6. A major thrust plane above may, and probably always does, originate 
in a fold below. 
7. A thrust plane may branch into smaller thrust planes, or pass into an 
overfold along the strike. 
8. The front portion of a mass of rock being pushed along a thrust plane 
tends to bow forward and roll under the back portion. 
9. The more rigid the rock the better will the phenomena of thrusting 
be exhibited. 
*H. M. Cadell, “Experimental Researches in Mountain Building,” Trans. Roy. 
Soc. Edinburgh, XXXV (1890), 337-57. 
