114 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



difference of resistance between the earlier and the later andesite is not great, so 

 that the slope is more uniform. The fact that the contours on the southwest corner 

 of the Mizpah Hill fault block are parallel to the contact of the softer lake beds 

 shows the minuteness with which the relief has been determined by the rock 

 resistance. 



EFFECTS OF FAULTING UPON THE TOPOGBAPHT. 



The effect of faulting on the topography in general is comparatively unimpor- 

 tant. The two earlier andesite hills above mentioned are the most conspicuous 

 cases where faulting has been (though indirectly) a factor. The volcanic (dacitic 

 and rhyolitic) agglomerates and tuffs, which, by the accidents of faulting, usually 

 adjoin faulted blocks of the Siebert tuffs in the southern half of the map, are 

 not much harder than these. Nevertheless, the lake beds (Siebert tuffs) are 

 undoubtedly the most easily eroded of all the formations, and areas occupied by 

 them are characterized for the most part by a smooth, flat surface, bounded 

 frequently by a slight scarp where the tuff adjoins more resistant rock. In most 

 cases, however, as is shown by the map, the tuff block is surrounded on all sides by 

 the harder blocks, and as there is no outlet for eroded material the tuff block can 

 not be now much below the harder blocks. 



