BETWEEN IRON-DOME AND MIKE FAULTS. 247 



Dome, Rock, and La Plata mines, the former of which is an incline fol- 

 lowing down the contact to the east, and the two latter tunnels running in 

 at or near the contact, in a southerly direction. On the steep hillside, at the 

 mouth of the Rock tunnel, stood once a huge outcrop of hard carbonate, 

 from which was obtained the first ore of this character found in the region. 

 A short distance above the contact, on Dome Hill, is an intrusive sheet 

 of Gray Porphyry, which, on the western point of the outcrop, cuts up into 

 the White Porphyry, but in California gulch comes actually in contact with 

 the limestone, arid at the La Plata mine cuts into it so that a small de- 

 tached portion of the limestone is left above this intrusive sheet. It also 

 extends up the south slope of Iron Hill, parallel to the contact, and only 

 separated from it in places by a thin sheet of green Lingula shales, which 

 belong to the Weber Shale formation. At the foot of the steep slope of 

 Iron Hill, opposite the Rock mine, the Blue Limestone is laid bare in the 

 quarry of the Montgomery claim. 



South slope of iron Hill. The steep north slope of California gulch, from 

 here down to the Iron fault, which crosses the gulch at the Garden City 

 mine, presents actual outcrops of the lower Paleozoic formations, the Blue 

 Limestone, Parting Quartzite, White Limestone, and Lower Quartzite, 

 together with an intrusive sheet of Gray or Mottled Porphyry near the 

 bottom of the Blue Limestone. In point of fact, these outcrops are covered 

 by from six to ten feet of slide material, but are readily seen in the numer- 

 ous prospect holes which dot the side of the hill. The dip of the limestone, 

 as shown by the various inclines on Iron Hill, varies from 12 to 25, while 

 its strike is more nearly north and south than the average strike of the sedi- 

 mentary beds throughout the region. In the Iron mine itself the dip shal- 

 lows as it is followed into the hill, and becomes, beyond the Tucson shaft, 

 nearly horizontal ; while in the Horseshoe shaft, at the head of Nugget 

 gulch, which has reached the contact at a depth of 482 feet, the limestone 

 is said to have dipped 8 to 10 to the southwest, showing a tendency to a 

 synclinal structure in this block of ground, which is still more marked in 

 the block next west. The Colonel Sellers shaft and drill-hole, south of this, 

 near the mouth of Nugget gulch, had not yet reached the contact. 



