BETWEEN BALL MOUNTAIN AND WESTON FAULTS. 221 



Iowa fault. — The Iowa cross-fault runs east and west along the foot of 

 the clift', on the north face of Upper Long and Derry Hill, and connects Wes- 

 ton and Ball Mountain faults. The shafts and tunnels between it and the 

 bed of the gulch are either in Weber Grits or Pyritiferous Porphyry, while 

 Archean granite forms the cliff above it on the south. The estimated dis- 

 placement of this fault is an upthrow of 2,7U0 feet to the south. It might 

 perhaps be better considered a downthrow to the north, since that portion 

 of the area which immediately adjoins it on that side is in the abnormal \)0- 

 sition of being relativel}^ lower than the corresponding block of ground on 

 the west of Weston fault. 



The uplifted block of ground inclosed by Iowa and Weston faults 

 consists of Archean rocks, principally coarse red granite, with a narrow 

 strip of Lower Quartzite resting on them along the crest of upper Long 

 and Derry Hill. This quartzite is apparently the crest of a shallow north 

 and south anticlinal fold, now almost entirely eroded away. The curve 

 of the strata can be readily seen on the cliff from Iowa gulch; at the 

 western end, toward the fault, the dip steepens to 30°. At the eastern end, 

 on either side of the ridge, is an outcrop of a much decomposed, coarse- 

 grained quartz-porphyry, which apparently forms a sheet between the 

 quartzite and underlying granite. 



Southwest slope of Ball Mountain. — From lowa fault uorthward, across Iowa 

 gulch and up the southwest slope of Ball Mountain, the surface is mainly 

 covered by Pyritiferous Porphyry, with occasional outcrops of the sand- 

 stones and shales of the Weber Grits. The sedimentary beds all have a 

 gentle dip to the northeastward and are separated by intervening porphyry 

 sheets into three distinct series, the lowest of which is classed as Weber 

 Shales, although black shales are found to a greater or less extent through 

 all the beds. 



This lowest series, which crosses Iowa gulch opposite the Ella Beeler 

 tunnel and extends part way up the slope of Green Mountain, comes in 

 juxtaposition with the White Porphyry beyond the fault to the west, and 

 is overlaid by a thin body of Pyritiferous Porphyry, which is cut in a 

 tunnel (E-21) on the slope of Green Mountain. 



