432 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



the outlines of ore bodies and contact may be less exact than in other 

 mines. There seein to be two ridges in the formation, marked by sudden 

 descent of the ore bodies to the east on the line of tlie section (E), but 

 along the Evening Star line, above the general steepening of dip at the 

 east limits of the bonanza, the inclination is more regular. The vein mate- 

 rial in this ground extends to depths of thirty and forty feet below the 

 contact, its total thickness not being in all cases ascertainable, as explora- 

 tions are seldom extended in depth as far as the unaltered limestone. The 

 rich ore bodies are generally found in its upper part, near the contact. The 

 former is generally soft and clayey, sometimes, however, a hard silicious 

 hematite, and in the vicinity of the ore bodies often a granular quartz, not 

 unlike a c^uartzite in general appearance. In the Main shaft 40 feet of vein 

 material was passed through before reaching unaltered limestone. This Avas 

 barren, with the exception of a thin streak of galena, carrying 379 ounces 

 of silver to the ton. The limestone below is of dark color, generally hard 

 and crystalline, but sometimes soft and pulverulent, containing clay infil- 

 trated through from above. 



From the bottom of the New Discovery shaft the ore extends in a 

 somewhat irregular body one to three feet in thickness to the northeastward, 

 and along the Evening Star line is practically continuous eastward as far 

 as the so-called ' ' crib." In the direction of the Main shaft its continuity for 

 a short distance is broken, but it comes in again in the northeast continua- 

 tion of the Crescent body, increasing in thickness toward the "crib" on the 

 Evening Star line, at the extremity of the drift running north from the Main 

 shaft. At the " crib," so called from the structure, filled with waste, used 

 to support the roof of the ore chamber, there is a sudden steepening of the 

 ore body on both sides of the line between Catalpa and Evening Star. An 

 almost solid mass of carbonate ore, 40 feet thick, was taken from this cham- 

 ber. It was difficult to obtain definite data as to the bounding rocks, but it 

 is evident that this deepening is due, not to a fold in the limestone, but to 

 replacement action extending a little deeper, probably along some fissure 

 or cleavage plane in the limestone. The general outline of the ore body 

 here is shown in the longitudinal Section A, Atlas Sheet XXIX, whose line 

 passes through this portion of the mines. 



