CONCERNING THE PROCESS OF THRUST FAULTING 



431 



under continued compression. A column may crumple into many 

 folds or it may spring out into a single arch. The second case is 

 stable for unsupported columns, but in the case of the earth's 

 crust the formation of many folds is common. Mechanically the 

 analysis of the stresses in one fold of a series is the same as that in 

 a single arch. The maximum tensional stress is at the apex of the 



Z3 - 



(c) 



Z) 



(<i) 



Fig. 5. — Paraffin members which failed under rotational stress, (a) and (ft) 

 are two views of a piece AXst^XZi'V inches in size, which yielded by combined com- 

 pression and bending. Compare Figure 2 and note the place of rupture along the 

 plane of maximum shear parallel to the surface, (c) is a side view of a piece 117X41*5^ 

 X 2 1*^ inches which seemed to fail by mere compression; the break indicated by dotted 

 Unes followed several high-angle breaks, {d) is a side view of apiece TffX2y%X2^'*5 

 inches in size which ruptured without flexing. Note the tendency toward high- 

 angle breaks. 



arch at the surface, the maximum compression beneath the apex 

 of the arch at the bottom of the deformed member, the focus of 

 maximum shear a plane containing the axis of the member and 

 parallel to the plane of greatest length and width of the member 

 (Fig. 65, S-S). A bending member which yields to shear alone 

 splits from end to end along a plane of maximum shear, a similar 



