22 WALTER H. BUCHER 
symmetrical joint planes points to the action of compressive stress 
in a perpendicular direction, or especially to the horizontal tensile 
Fic. 20.—Block diagram representing the pitching end of an anticline. 
Sec. a-a’=sec. 1 below. 
Sec. b-b’=sec. 2 below. 
These sections show, in addition, the position of two inclined joint planes striking 
parallel to the axis of the fold. Sec. A shows the result of squeezing out the shale 
layers from underneath the joint plane in such a way that the lower portion of sec. 2 
is pushed out so as to rest under the upper portion of sec. 1. 
stress which results when the upper layers are forced up by the 
pressure of the flowing layers of shale underneath. 
Whenever a stream removes a portion of such an anticline, as 
indicated on the map sketch in Figure 18, the tendency exists to 
