FAULTING. 77 



any definite continuous scarp. Moreover, the jogs in the scarp under considera- 

 tion can not he explained by stream erosion, for they are not at the entrance of 

 auxiliary gullies, the angle of the jog forming practically an unbroken wall. 



ZIGZAG SCARPS EXPLAINED BY FAULTING. 



The phenomenon described can hardly be explained except as controlled by 

 faulting, and two intersecting systems are indicated. Corroborative evidence of 

 this conclusion is present. Along the western portion of the scarp where 

 examined there occur at different points isolated outcrops of light-colored dike 

 rhyolite that has the characteristics of the Oddie rhyolite, and is distinct from 

 the glassy Tonopah rhyolite-dacite with which it is in contact. These dikes are 

 intermittent rather than continuous, but form distinct jogs parallel with the set- 

 offs of the scarp. It is known that this rhyolite sometimes forms dikes along 

 faults in this district and is later than the main faulting. 



CONSEQUENCES OF EXPLANATION. 



The chief or longer scarp faces are parallel to the straight scarp into which 

 the jogged scarp runs farther east (j?, in PI. XII), while the shorter or minor 

 faces are parallel with the slight scarps lying a short distance farther north, 

 limiting probable fault blocks, as already described. It appears, then, that the 

 jogged scarp is the result of two sets of intersecting faults, and from the figure 

 it is evident that when the dimensions of the jogs are diminished the course 

 of the resultant will approach a straight line, and indeed may do so to such 

 a degree as to be practically indistinguishable from such a line. By the pre- 

 dominance of one set of faulting over the other set the resultant line may lie in 

 any given direction and may be straight or curved. The line made by joining 

 the points of the sharp spurs along the scarp, indicating the general resultant 

 of the two systems of jogs, is parallel with the scarp first mentioned, which 

 lies farther east (A, in PI. XII). It is possible, therefore, that this last named 

 straight scarp may actually be a resultant of two intersecting systems, such as 

 have been described. 



ZIGZAG FAULT SCARP ON TONOPAH-SODAVILLE ROAD. 



On the north side of the main road which leads from Tonopah toward Soda- 

 ville, in the western part of the area mapped, a similar phenomenon was noted. 

 The road lies in a depression, on the south side of which there is an irregular, 

 undecided embankment consisting mostly of fragmental material and having a 

 height of about 10 feet. On the north side there is a sharp scarp about 25 feet 

 high, consisting of a continuous outcrop of solid, glassy Tonopah rhyolite-dacite. 

 On inspection this scarp shows well-marked rectilinear courses, forming steps 



