58 



GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



W Match section ; 30,000 feet; conformable. 



CAMBKIAN. 



Lower Quartzite. The beds assigned provisorily to this horizon, which are 

 indicated on the map in a dark-purple color (6), are prevailingly of quartz- 

 ite. To them, therefore, the local name of Lower Quartzite has been given. 

 Their average thickness is about one hundred and fifty feet to two hundred 

 feet, of which the lower one hundred feet are composed of finely and rather 

 thinly bedded white saccharoidal quartzites, while the upper fifty feet are 

 shaly in character and more or less argillaceous and calcareous, passing by 

 almost imperceptible transition into the silicious limestone of the Silurian 

 formation above. 



At the very base of the series, at the contact with the underlying Archean, 

 wherever this could be observed, is found a persistent bed of fine-grained 

 conglomerate, from a few inches to a foot in thickness, made up of rounded 

 and finely polished grains of bluish translucent quartz, generally not larger 

 than a pea in size. Above this is a white quartzite of remarkably uniform 

 and persistent character, always very readily distinguishable as a white 

 band in the numerous sections offered by the canon walls of the range. Its 

 thickness, when measured on the west side of the range, or near the Sawatch 

 island, is, as mentioned above, 100 feet of purely silicious beds. On the 

 east side of the range the thickness seems somewhat to diminish, and in 

 places was found to be only 40 feet. 



In Buckskin canon a thin bed of silicious limestone was found included 

 in the quartzite. The rock of this bed is remarkable as containing rela- 



