LOW-ANGLE FAULTING II 
and overthrust structure of the Alps... With this end in view 
Paulcke adopted a stratigraphic series which, in most cases, com- 
prised a thick basal layer of sand, above which were eight or nine 
alternating layers of clay and plaster. The mass was then weighted 
above by a very thick covering of sand. Because of the nature of 
the materials, fracturing of quite variable sorts developed—both 
typical reverse faults and a few low-angle overthrusts in which 
a strong plaster bed carrying the thrust was shoved bodily over the 
less competent clayey material beneath. But the brittle layers of 
plaster broke into numerous small rectangular blocks in addition 
to the major folding and faulting, and these small blocks were so 
rotated, shattered, and irregularly displaced as to mask much of the 
more significant behavior of the strata under compression. In 
general outlines, however, various cross-sections of the Alps were 
reproduced. 
The experiments of Cadell suggested that the piling up of 
weight may be an important factor in determining the low-angle 
overthrusts, and that perhaps the question may be solved by expeti- 
mentation. This stimulated us to attempt further experimentation 
in an effort to determine the influence of various contributing 
factors upon the angle of faulting. 
- METHODS OF PRESENT EXPERIMENTAL INVESTIGATION 
Apparatus—For these studies a pressure box was constructed 
along lines similar to those adopted by Cadell and Willis (see Fig. 4). 
This box differed, however, from the previous ones in having screws 
and movable pressure blocks at both ends, instead of solely at one 
end. Pressures could thus be applied from opposite directions 
whenever desired. But it was found, early in the progress of the 
work, that these pressure blocks frequently manifested a strong 
tendency to rise up from the floor of the box and to become tilted as 
the faulting of the strata progressed. To prevent this, long steel 
guide flanges were bolted on the inner sides of the box at a height — 
cf about an eighth of an inch above the top of the pressure block. 
With this control the pressure block could only move forward 
and backward, and the tilting of the block was thus practically 
W. Paulcke, Das Experiment in der Geologie (Berlin, 1912), pp. 74-108. 
