VALLEY VIEW VEIN SYSTEM. 139 



fault that the truth of the hypothesis may well be doubted. Another possible 

 hypothesis may be formulated. Comparison of the vein in the main Valley View 

 workings and in the outcrops shows that near the surface the strong north- 

 dipping vein underground changes by branching into a number of vertical veins, 

 which are strong, yet not so strong as the main veins. In the Stone Cabin and 

 Silver Top workings these vertical veins extend far deeper than on the Valley 

 View side of the fault and no flat vein has been encountered. It follows as a 

 satisfactory explanation that the veins on the east have been dropped down by 

 the fault vertically, so that the upper vertical portions come opposite the lower 

 flat portion on the west. 



It is not easy of explanation on either hypothesis why the fault has not been 

 recognized on the surface. Especially under the hypothesis of rotation or differential 

 tilting is this fact inexplicable, for such rotation must have been likewise manifested 

 at the surface as a great and sustained difference in the vein dips; whereas actually 

 no such change occurs, the steep, nearly vertical, dip being unvarying over the area 

 which the fault would naturally cut. If, however, according to the second hypothesis 

 of simple downward displacement, the movement is assumed to have been absolutely- 

 vertical, there is at least a possible explanation of the failure to detect the fault 

 namely, that in the surface portion of the group the vertical veins, broken by a 

 vertical fault, would not show any displacement, while below, where the. vertical 

 veins come opposite the flat ones, the displacement would be marked. 



The probability of this latter hypothesis is strengthened by a consideration of 

 the main Stone Cabin fault, which has a general parallelism in strike and dip with 

 the Valley View fault, and lies about 250 feet horizontally east of it. This fault is 

 a normal one, having a heavy downthrow on the east side, bringing the tuffs, and 

 below these the later andesites, opposite the earlier andesite of Mizpah Hill on the 

 west. It is probable that a near-by parallel fault, like the Valley View fault, would 

 have a movement in the same direction. The Valley View fault is evidently much 

 the smaller of the two, and may, indeed, be considered auxiliary to the main 

 displacement. 



Amount of vertical separation of Valley View fault. The amount of vertical 

 movement at the Valley View fault, on the basis reached above, would be something 

 over 400 feet. This affords some basis for understanding the movement on the 

 greater Stone Cabin fault, which may reasonably be expected to be several times 

 greater. 



