222 GEOLOGY AND MINING INDUSTEY OF LEADVILLE. 



The base of the Weber Grits, consisting of quartzite, conglomerate, 

 and shale, is shown on the south side of Iowa gulch in the Little Hercules 

 tunnel (E-6), and on the north side in the Black Cloud shaft, which cuts 

 through it into the underlying porphyry. On Green Mountain the Hoo- 

 sier (E-19) and adjoining (E-20) shaft are sunk in it, and the Equator 

 (E-17) tunnel runs on the contact breccia material between it and a sec- 

 ond sheet of Pyritiferous Porphyry above. The outcrops of this body, 

 consisting of iron-stained decomposed porphyry, can be easily traced along 

 the slope of Iowa gulch, but the underlying Weber Grits are obscured by 

 debris. South of the gulch it is shown in the Mount Carbon tunnel and on 

 Green Mountain in the Tiger shaft and in the Ontario and Bloomington 

 (E-9) tunnels. The former passes at 200 feet from its mouth into mica- 

 ceous sandstones and shales of the second sheet of Weber Grits, while the 

 shaft (E-18) shows breccia material between the sandstones and the under- 

 lying porphyry. 



The outcrops of the second body of Weber Grits sweep round the 

 upper part of Green Mountain, where the Green Mountain and Lawrence 

 (E-10) 1 shafts have reached it after crossing the lower part of the upper 

 body of Pyritiferous Porphyry; it widens out in the vicinity of the Little 

 Frank (D-2) shaft and the Alleghany and Pine Forest tunnels, and again 

 thins to thirty or forty feet as it crosses Iowa gulch to the Iowa fault below 

 shaft D-4. Above this body of Weber Grits the main sheet of Pyritifer- 

 ous Porphyry extends up to the crest of Ball Mountain and east to the 

 fault, broken only by isolated outcrops of Weber Grits, apparently repre- 

 senting fragments of this formation caught up in the mass of the porphyry 

 at the time of its intrusion. Such a fragment, consisting mainly of black 

 shales, is cut in the Silver Queen tunnel on the hill slope above the Pine 

 Forest. 



The weathered surface of the Pyritiferous Porphyry in general shows 

 no pyrites, but only the cavities from which its crystals have been dis- 

 solved out. The old Mariner tunnel, above the Silver Queen, has been run 

 125 feet from the surface in porphyry thus decomposed, and at the mouth 

 of the former is a deposit of needles of spruce, cemented together and partly 



'Wrongly named Leaven worth on the index sheet of the Atlas. 



