406 GEOLOGY AXD MINING INDUSTRY OF LEADYILLE. 



White Porphyry are then crossed, these being Hkewise very difficnlt to 

 distinguish from each other underground. At the Blue Limestone contact, 

 which occurs at the bottom of the Loker shaft, no ore is found on the tunnel 

 level. A drift runs off to the eastward about one hundred and twenty-five 

 feet from the Loker shaft, through which the ore stopes both above and 

 below are reached. From the Loker shaft the tunnel runs for aljout five 

 hundred feet in the Blue Limestone, which has an average dip of 15° to 20° 

 to the southeast. Wherever raises have been made to the porphyry above, 

 barren vein material has been found. This also reaches the tunnel level at 

 times, following bedding or joint planes in the limestone. In one case a 

 drift and winze have followed a considerable mass of vein material in the 

 limestone, but without finding pay ore. Near the end of the tunnel the 

 normal contact between limestone and porphyrj- is crossed. The limestone 

 is here of lighter color, seamed with white calcite, and somewhat brecciated. 



At the bottom of the Hynes shaft, with which the tunnel is intended 

 to connect, drifts have been run upon the contact, disclosing some vein 

 material. The dip of the formation is here shallower and to the southward. 

 Above the contact are found quartzite and shales, belonging to the Weber 

 Shale formation, between it and the White Porphyry, as in the Bull's Eye 

 and Lime claims. 



While the pay ore in this mine has been found at the contact, not of the 

 Blue Limestone, but of ihe Parting Quartzite, it does not, so far as known, 

 extend between these two formations. This would readily be accounted for 

 on the theory that these ore bodies are the replacement of a portion of Blue 

 Limestone left between the Parting Quartzite and the White Porph3'ry at 

 the time of the intrusion of the latter. 



Adelaide. — The Ore bodics in the Adelaide mine are much more discon- 

 nected and irregular than in the Argentine. The mine has been mainly 

 worked by a number of isolated shafts, and owing to complexity of the 

 geological structure the ore bodies have not been systematically followed, 

 so that, as many drifts were closed at the time of visit, the geological data 

 are less complete than could be desired. The main difference in the forma- 

 tion between this and the Argentine is the occurrence of a later intrusive 

 sheet of Gray Porphyry between the White Porphyry and the Parting 



