STRUCTURAL RESULTS OF FAULTING. 185 



action has succeeded, as well as preceded, the deposition of the ore and 

 gangue. The regularity of the curve, on the other hand, shows that tlie origi- 

 nal surface line along the Sutro section was sensibly straight, and lay on a 

 gentle western slope. The agreement of the contours of the range with 

 those of the west wall and of the cross-sections with the curve obtained 

 from theoretical considerations, proves that the erosion since the commence- 

 ment of the faulting action is sensible (on a scale of 800 feet to the inch) 

 only where most intensitied — i. e., in the ravines. The faulting and the depo- 

 sition of ore have therefore occurred since the District was subjected to any 

 considerable amount of general degradation. The level condition of the 

 country prior to the fault appears to me probably the result of erosion, and 

 if so the District must have been a plateau or a high mountain valley — in 

 short, an area of denudation. 



Fault probably the result of a rise in the west country. It Is pCl'liapS ImpOSsiblc tO demon- 

 strate whether the absolute movement involved in the faulting was the rise 

 of Mount Davidson, or a sinking of the east country. If the east country 

 has sunk, the former level near the middle of the Lode must have been 

 nearly that of Mount Davidson, and the District must have occupied the 

 crest of a rather sharp undulation running nearly east and west. If the 

 main movement was an uplift of Mount Davidson, and its neighbors to the 

 north and south, the original general level was al)out that of the present 

 coimtry east of the Lode. The District must then have been near the top 

 of a gentle undulation approximately parallel to the Sierra. The latter 

 supposition accords with the general character of the present topography of 

 the Great Basin area much better than the former, and seems to me much 

 more probable on general as well as local grounds. 



Diminution of evidence of fault near the ends of the Lode. To tllC llOrtll aud SOUtll of 



Mount Davidson the evidence of faulting diminishes. From the Overman 

 far into the Sierra Nevada claim, a distance of two and one-tliird miles, the 

 amount of fault has been great, and the indications are unmistakable. Be- 

 yond these points the disturbance of equilibrium has been to some extent 

 adjusted in a different manner. This is partly indicated on the surface map 

 by the union of the andesite fields, which are separated opposite the middle 

 portion of the Lode by diorites. Towards the ends of the Lode the dynamic 



