BETWBE:!Sr MOSQUITO AND BALL MOUNTAIN FAULTS. 215 



East Ball Mountain. — The ci'est of wluit is kiiown as East Ball Mountain, 

 which is in reality only a spur of West Dyer Mountain, is capped by Lower 

 Quartzite, with a sheet of AVhite Porphyry between it and the underlying 

 Archean. This sheet is evidently the same which has already been noticed 

 on the south spur of Dyer Mountain; in the recess of Dyer amphitheater, 

 however, it must cut partly across the Lower Quartzite, since on the west 

 wall of the amphitheater there is a considerable thickness of Lower Quartz- 

 ite below the White Porphyry. 



AREA BETWEEN MOSQUITO AND BALL MOUNTAIN FAULTS, 



Ball Mountain fault. — The direction of the Ball Mountain fault is some- 

 what to the west of north, nearly parallel with that of the Weston fault, 

 and therefore convergent with the Mosquito fault, which it joins on the crest 

 of the Upper Long and Derry Ridge at the foot of the steep slope of West 

 Sheridan. From here it runs in a direct line across Iowa gulch, through 

 the top of Ball Mountain, and bends sharply to the west on its northern 

 slope, passing through the End Squeeze or Cleopatra shaft (F-12).' Its 

 movement is defined here by the Fat Purse (F-17), which is in Weber Grits 

 on the west of the fault, and the John Mitchell (E-11), which is in Lower 

 Quartzite on the east; it then runs northward across South Evans gulch, 

 through the Nevada tunnel, which has been driven nearly three hundred 

 feet on its line, and just west of the Seneca shaft, which is in the White 

 Limestone. Farther north its existence is shown only by the widening of 

 the outcrop of Weber Shales and by a slight discrepancy in the outlines 

 of the body of Mount Zion Porphyry in Evans gulch. Its movement of 

 displacement is an upthrow on the east, which has a maximum at the south- 

 ern end, or in Iowa gulch, of 2,250 feet, and gradually decreases to the 

 northward, being only a few feet in Evans gulch and disappearing entirely 

 in Prospect Mountain. 



Prospect Mountain Ridge. — Qn the spur from Prospcct Mountain west of 

 the Prospect amphitheater, which is on the line of the fault, there is a slight 

 variation in the regular easterly dip of the Weber Grits, which suggests 



' Tlio letters aud numbers following tbo n.ames of shafts indicate, respectively, the square and 

 tbo uiuubcr within that square, by means of which the shaft may be found on the Leadville map. 



