CONCERNING THE PROCESS OF THRUST FAULTING 429 



mation member, and vertical fault planes of a comparable origin 

 are not commonly recognized. 



Experiments with short blocks under rotational stress. — Experi- 

 ments with^ paraffin led to somewhat different results. The 



Fig. 3. — (a) and (b) are two views of a sheet of soap which failed by combined 

 compression and bending under rotational "stress. The dimensions of the piece of 

 soap are i%X42X2§ inches. The contour intervals are j\ inch, indicating the plane 

 of rupture. A photograph of the piece is reproduced in Figure 2. (c) is a cross- 

 section of another piece of soap showing a similar rupture. The dimensions are iVX4i^jr 

 X2y% inches. 



paraffin members did not flex so readily as soap, and therefore, in 

 spite of their dimensions, they approach the behavior of short 

 blocks under the conditions of these experiments. The members 

 did not break from the bottom to top but after a few preliminary 

 high-angle sUce faults part of the members seemed to chip out 

 (Fig. 5, c and d), illustrating the manner in which weak unbend- 

 ing blocks yield under a rotational compression.^ However, having 



' In experimental engineering any cement block which is loaded with an unequally 

 distributed load fails by breaks, making low angles with the direction of applied force. 

 Such breaks are considered faulty, because the object of that work is to determine the 

 strength of the blocks under equally distributed stress. 



