430 GEOLOGY AND MINING INDUSTEY OF LEADVILLE. 



of Erin and Brookland claims. It obtains its maximum breadth of about 

 two hundred feet and a thickness of pay ore of over fifty feet in the Even- 

 ing Star ground, vein material having here replaced apparently the entire 

 thickness of the Blue Limestone, which, as a result of this action, has 

 shrunk to about one hundred feet. As in the Carbonate body, there is a 

 noticeable steepening in the dip of the formation beyond the eastern limits 

 of the ore current, but the amount of replacement by oxidized material has 

 been so great that the minor waves in the limestone are difficult to trace. 



It were too long to enter into a detailed description of the workings 

 in each mine, as has been done in the case of the Carbonate ; and, since the 

 map and sections represent, so far as their scale permits, the results of thor- 

 ough examination of every drift, only the salient points and general features 

 will be mentioned in what follows. 



Crescent mine. — The Cresceut, like the Carbonate mine, is worked through 

 a long incline, following the dip of the stratification. In this case, how- 

 ever, the angle of the incline varies from point to point in an attempt to 

 keep on the contact; but, owing to the irregularities of the limestone surface, 

 it runs, like the former, now into the limestone foot-wall and again into the 

 porphyry above. Its average angle is at first 12" to 13°, but 50 feet beyond 

 the No. 3 shaft it becomes 20° to 25°, continuing on this average slope 

 to a distance of 800 feet from the mouth. For the first 80 feet it runs in 

 Wash, composed of clayey gravel inclosing rounded bowlders of Sacra- 

 mento Porphyry ; above the contact are four feet of quartzite, supposed to 

 belong to the Weber Shale horizon. This quartzite is very generally found 

 below the porphyry in this and the adjoining mines to the north. It is 

 ordinarily very thin and difficult to distiiiguish from the porous quartz 

 which frequently constitutes the gangue or vein material. As in the Car- 

 bonate mine, the dip of the limestone is very shallow near the surface, and 

 it is possible that it forms here as there the crest of a fold, but the explora- 

 tions in this region were unfortunately too few to afford definite data on this 

 point. 



The main ore body is developed between the first and fourth levels 

 and extends from the incline in a northeasterly direction to the Catalpa 

 line. South of the incline, it was found only on the first level, extending 



