484 GEOLOGY AND MESTING INDUSTRY OF LEADVILLE. 



been eroded off and the- ore body extends up to the Wash. A thin quartzite, 

 evidently belonging to the Weber formation, is often found directly above 

 the ore horizon. The main ore body was almost perfectly continuous, 

 varying in thickness from a few inches up to twenty-five feet, and generally 

 overlaid as well as underlaid by dark-blue chert. At the time of visit a 

 layer of ore was being followed which consisted of barite thoroughly im- 

 pregnated with chloride of silver. The rich ore is sometimes a red sandy 

 or clayey mass, and sometimes consists of chert or silicious iron, whose 

 cracks and joints are lined with chloride of silver. The ore in general," as it 

 comes from the mine, is characterized by its bright-red color, due to the 

 presence of anhydrous iron and absence of manganese oxide. 



The principal working shaft of the mine at time of visit was the 

 No. 2, from which two levels were run; the old No. 1 or Ladder shaft was 

 no longer used for the extraction of ore, and the new shaft to the northeast 

 of these, designed to open the ore body on the dip, was not yet working. 



The main thickness and the richest portion of the ore body lay to the 

 south of shafts No. 1 and No. 2, between these and the dike. Directly 

 south of No. 2 is a small irregular sheet of Gray Porphyry, cut in the lower 

 level in a thickness of four to six feet, which seems to run partly with the 

 stratification and partly across it. Too little of this body was exposed to 

 afford sufficient data for determining its extent or origin, but it evidently 

 acted favorably on the concentration of ore in its vicinity, probably by 

 arresting the flow of the ore-bearing solutions and giving them time to pre- 

 cipitate the minerals they held in solution. The drifts in the western part 

 of the mine had been extended south until they reached the porphyry dike, 

 but, singularly enough, in the eastern part of the mine they stop before go- 

 ino- so far south, it seeming to have been taken for granted that the dike 

 would cut off the ore indefinitely in that direction ; whereas there is every 

 reason to believe that at no great distance to the eastward it will continue 

 south over or across the line of the dike. It is hardly necessary to say that 

 the outlines of the eastern end of the dike, as given on the map, are conse- 

 cpientlv founded only on general probability, there having been no explo- 

 ration to determine its exact limits. The ore horizon in the Lee ground has 

 a relatively steep dip to the northeast, which may be taken as averaging 



