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WALTER H. BUCHER 



of shearing for this grouping of stresses is represented diagram- 

 matically in Figure 8; Figure 9 illustrates the occurrence of this 

 type in nature on a small scale/ It shows "symmetrical faults" 

 in a hard encrinal layer a foot or two in thickness in the Hamilton 

 shales, exposed along the shores of Cayuga Lake. "The exposures 

 of this layer along the lake show faults every few feet." "The strike 

 of the majority is from 20-25° north of west." "Their inclination 

 is sometimes south and sometimes north and the angles are nearly 



Fig. 8. — Diagram illustrating the position of the planes of shearing in a brittle 

 body subjected to compression in a horizontal direction with the direction of easiest 

 relief (least principal stress) vertical. 



the same in the two cases, making the faults symmetrical about a 

 nearly horizontal plane." "The hade varies from 45° to 75°, but 

 most are near the average, which is 62°." The fault surfaces are 

 slickensided and covered with strong, even striations. "The 

 vertical displacement along these faults is from a fraction of an 

 inch to three inches." The faults "usually continue for a few 

 feet in the adjacent shale, but instead of continuing with the same 

 hade, they flatten out and become nearly horizontal in the shales 

 where no hard layer is present."^ 



' Pearl Sheldon, "Some Observations and Experiments on Joint Planes," Jour. 

 Geol., Vol. XX (1912), Fig. 3, p. 61. 



^ Ibid., pp. 60-62. . 



