60 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



One of the most interesting features of this series is the local develop- 

 ment of serpentine, resulting evidently from the metamorphism of pyroxene 

 and amphibole. It has been found in small quantities at various points, but 

 is developed on a very considerable scale in the Red Amphitheater in Buck- 

 skin gulch, where it forms a remarkably beautiful verd-antique and a pecul- 

 iar massive yellow rock, resembling bees-wax not only in color but also in 

 texture. 



Fossils. The only fossil remains found in this series occur in a bed of 

 greenish chloride shales on the east flank of Quandary Peak, about a mile 

 above the Monte Cristo mine. They belong to the genus Dicellocephalus, 

 and resemble closely Dicellocephalus Minnesotensis of the Potsdam formation. 



Owing to the thick covering of forest immediately east of the point 

 where these fossils were found, it was impossible to fix with absolute cer- 

 tainty the exact horizon of the bed in which they occur. They are imme- 

 diately above a heavy white quartzite, and beneath a bed of white marbleized 

 limestone, which is in turn overlaid by the quartzite which carries the Monte 

 Cristo ore deposit. From analogy with other sections, however, it seems 

 safe to assume that it occurs above the main body of quartzite and near the 

 base of the transition series. 



SILURIAN. 



The beds assigned to this horizon consist of light-colored, more or less 

 silicious, dolomitic limestone, capped by beds of quartzite of varying thick- 

 ness which mark the dividing line between it and the overlying formation. 

 On the general map of the Mosquito Range the entire series is included in 

 one color-block (c). On the more detailed maps two divisions are made, 

 to which the local terms White Limestone (c) and Parting Quartzite (d) 

 have been given. 



white Limestone. The beds to which this local name has been given, 

 from their prevailing light color as distinguished from the dark blue-gray 

 or even black limestone above, consist in the main of light drab dolomites, 

 and contain, besides the normal proportions of carbonates of lime and 

 magnesia, from 10 per cent, upwards of silica. They are generally rather 

 thinly bedded, of compact rather than crystalline structure, and frequently 

 have a conchoidal fracture, approaching a lithographic stone in texture. 



