LOW-ANGLE FAULTING AI 
under the heavily burdened portion (see Fig. tg). But in these 
experiments the loads were relatively light. 
A load light in proportion to the horizontal stress will thus 
influence the angle of fracture, depending upon the ratio of vertical 
and horizontal stresses. A load very great in proportion to the 
horizontal stress will prevent faulting altogether within the loaded 
area. The influence of the load upon the angle of thrusting will 
therefore reach a maximum value somewhere between a load which 
- Fic. 19.—Effect of local weighting in locating the position of faults. The 
material to be faulted was clay stiffened with plaster; the added load was damp sand. 
In experiments of this sort the fracture plane most frequently appeared at the surface 
close to the edge of the piled-up overburden. 
is light and a load which is heavy relative to the horizontal stress. 
What the proper ratio for the maximum effect will be cannot well 
be determined until more is known of the limiting strength of rocks 
under stress.‘ Some idea, however, may be gained possibly by 
a rough inspection of the factors involved. The stress difference 
necessary to cause faulting at a given depth in the earth would 
need to be sufficient ‘to exceed the sum of the crushing strength of 
the given rock at the surface, plus the weight of overburden which 
must be lifted, plus again the increased strength of the material 
‘Louis V. King, “‘On the Limiting Strength of Rocks under Conditions of Stress 
Existing in the Earth’s Interior,” Jowr. Geol., XX (1912), 119-38. 
