MINES OUTSIDE THE LEADVILLE DISTRICT. 



535 



because it was recognized as the "Leadville contact" that the limestone 

 was prospected. The general geological structure is shown in Figure 5, 

 which represents an east-and-west section approximately along the northern 

 boundary of the area mapped. 



Figure 5. Taylor Hill. 



Weber Grite. 



Weber Shales. Blue Limestone. Parting Qu 



Gray Porphyry. 



The Cambrian, Silurian, and Blue Limestone beds here outcrop along 

 the base of the wooded hill slopes, dipping at about 20 to the eastward. 

 Above these is the main sheet of Gray or Eagle River Porphyry in great 

 thickness, the sandstones of the Weber Grits forming the upper part of 

 Chicago ridge. The lower part of the Weber Grits, or the Weber Shales, 

 which here consist mainly of quartzite, with only a few thin layers of 

 shale, are split into two portions by the porphyry body and separated from 

 the main body of Weber Grits above. A fragment of these, about forty 

 feet thick at the outcrop, is left resting directly on the Blue Limestone below 

 the porphyry body. The Blue Limestone has the ribbings of white calc spar, 

 which characterize it at Leadville and at the Sacramento mine. No ore has 

 been found at the actual porphyry contact, but it occurs at the upper sur- 

 face of the Blue Limestone, extending downward to a depth of 15 to 20 

 feet, as shown in Figure 6, which is a section on a larger scale through the 

 mine itself. 



As at Leadville, the ore occurs as a replacement of the limestone, but 

 yields free gold instead of lead and silver, the latter occurring only in small 

 quantity, and lead as yet not having been found. The vein material con- 



