EXPLANATION OF SECTIONS. 269 



upper Heurietl workings and the lower workings of the Waterloo claim, 

 and shows the anticlinal axis, which very nearl}' corresponds with the Car- 

 bonate fault, in the latter. .This axis, as already stated, is found to coincide 

 with the line of the fault farther north; and it is possible that on the line 

 of the section the fault movement may have already died out, since its actual 

 plane has not been proved.' Of the synclinal basin under Leadville in the 

 line of this, section the depth and angle of the formations on its eastern rim 

 are deduced from actual data, which are not, it is true, as complete as could 

 be wished The location of the svestern rim, however, is more theoretical. 

 Section F. — Sectiou F, on a slightl)- broken line, passes through the crest 

 of East Ball and Ball Mountains, from the latter across the slope of Breece 

 Hill to the head of Nugget gulch, through the middle of Iron Hill, and 

 along, the bed of California gulch, into the mesa country. East of the Mos- 

 quito fault it shows a patch of Lower Quartzite left on the crest of East 

 Ball Mountain. Between Mosquito faultandBall Mountain fault it shows the 

 development of White Porphyry in the lower horizons and its comparative 

 absence above the Blue Limestone ; between the converging Ball Mount- 

 ain and Weston faults, the great development of Pyritiferous Porphyry and 

 the probable continuation of the numerous sheets of White Porph3uy in 

 the lower horizons. The anticlinal structure shown in the eastern portion 

 of this block represents the supposed influence of the anticline observed 

 at the north base of Ball Mountain, which, owing to the curvature of the 

 line of Ball Mountain fault, is the proper continuation of this jJOi'tion of 

 the area. The distribution and thickness of the numerous bodies of por- 

 phyry in the latter block are deduced mainly from the data obtained in the 

 adjoining regions, since along the actual plane of the section, as will be evi- 

 dent from its examination, there are few data obtained from underground 

 workings. In the next block, between Weston and Pilot faults, a body of 

 Pyritiferous Porphyr}' is shown in section, whose thickness is largely a mat- 

 ter of conjecture, the only direct evidence being that of the Cumberland 

 shaft, near its northern edge, where it is 450 feet. As the plane of the sec- 

 tion probably cuts through the thickest portion of the body, the thickness of 



' Later developmeuts render it probable that the sheet of Gray Porpliyry is in the Blue Limestoue, 

 above the Hue of Carbonate fault, instead of at its base, as shown in the sectiou. 



