438 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



was considered by the miners a limestone bowlder. Explorations generally 

 stop in the iron body or barren vein material underlying the ore body. 

 The steepening of dip to the east of the ore body is very marked at the 

 present extremity of the incline, as well as near the bottom of the Upper 

 shaft; its angle is here 25. A fine body of carbonate ore is just being 

 opened to the west of this point. 



The old workings of the mine were reached from the Lower or Board- 

 ing-House shaft, and at time of examination were inaccessible. From infor- 

 mation obtained it appears that a large mass of vein material was found 

 here, and a layer of valuable ore at the contact, which reached the Evening 

 Star line on the south, but was cut off at 125 feet east of the shaft by a 

 break in the formation. This break was found, at the extremity of the west 

 drift from the Main shaft, to consist of an actual displacement of 20 feet in 

 the formation, bringing the basset edges of the limestone against a sheet of 

 Gray Porphyry, which here overlies the contact To the west of this there is 

 a sharp rise in the contact, which was explored with some difficulty through 

 drifts rendered dangerous by the plastic condition of the decomposed Gray 

 Porphyry. This body was found in no other workings, and what could be 

 determined of its outlines is shown in Section C. Where it comes up through 

 the limestone, as it undoubtedly must, is not therefore known, but a pos- 

 sible manner of offshoot from the main sheet below is shown in Section A. 1 



The normal continuation of this great ore body would be between the 

 Maid of Erin and Brookland shafts. In the former contact was struck at 

 385 feet and 15 feet of iron were passed through. To the north of the shaft, 

 in a drift rising between Gray and White Porphyry, was found a small 

 body of galena. The developments are as yet too limited to furnish an 

 accurate idea of the shape of this body of Gray Porphyry, which is there- 

 fore merely indicated in the section (B), as shown by present developments, 

 with no suggestion as to its probable continuation. Ore is also said to have 

 been struck in the Brookland shaft. The Big Chief and Clontarf shafts 

 have also reached the contact and found vein material and ore, but as yet 



1 Mr. Eicketts (op. cit., p. 41) states that a dike, eight to ten feet wide, crossing the limestone, 

 has siuce been cnt by one of the drifts of the mine, -which he regards as the feeder of this sheet of Gray 

 Porphyry. 



