120 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



sive sheets in the Archean and overlying Paleozoic beds. The results of the 

 rnetamorphic action are shown, not only in the decomposition and coloring 

 of the rocks above mentioned, but in the marbleizing of the limestones and 

 the large development of serpentine within these limestones. 



The eruptive bodies developed here consist, besides the large body of 

 Lincoln Porphyry near the summit of Mount Bross, first, of a considerable 

 body of augite-bearing diorite (96), which cuts through the Archean from 

 the valley below up into the bed of the amphitheater, and either spreads 

 out along the base of, or extends into, the Cambrian beds under the talus 

 slopes of debris ; secondly, of a dike of White Porphyry, crossing Silurian 

 and Carboniferous limestones in a vertical direction ; thirdly, of several thin 

 intrusive beds of green and much-altered quartz-porphyry, parallel with 

 the stratification. It is only on the south side of the amphitheater that a 

 continuous cliff-section of the Paleozoic beds is exposed, and here the top 

 of the Blue Limestone and the base of the Cambrian are each covered by 

 surface accumulations. One principal and several smaller faults can be 

 distinguished on the cliffs, in each of which the upthrow is to the west, but 

 the amount of displacement is only slight. The Colorado Springs mine is 

 opened on this cliff, near the base of the Blue Limestone, from which rich 

 ore in small quantities has been obtained. The following section was made, 

 by means of a pocket level, on the cliff just south of the mine and near (he 

 dike of White Porphyry above mentioned : 



Feet 



! Black cherty limestone 50 



Blue-gray limestone 50 



Ligbt-blue limestone \ 



hite marbleized limestone I GO 



^ Light drab limestone witli serpentine ' 



160 



White and greenish quartzite 40 



White limestone 10 



Light -bluish limestone 40 



Silurian 



Green porphyry, 20 feet. 



White limestone 10 



Blue-gray crystalline limestone ... 40 



. Light-colored limestone with serpentine 30 



170 



