LITTLE PITTSBURGH MINE. 469 



ished to 4 feet at 40 feet and to 18 inches at 70 feet from the shaft. In 

 the end of the south drift, underlying White Porphyry and overlying Wash 

 are both visible. An east-and-west drift explores the whole width of the ore 

 b.ody, reaching continuously into Little Chief ground. The body is nearly 

 level, and in the southern portion has a slight inclination to the south. Its 

 greatest thickness is from sixteen to twenty feet. Wherever its upper sur- 

 face has been reached, the Wash is found resting directly on it. West of 

 No. 1 shaft the underlying White Porphyry comes up to the level of the 

 east-and-west drift just south of that drift and dips gently to the northward 

 on the other side of the drift. East of the No. 1 shaft, near the boundary 

 of the claim, the ore horizon consists principally of chert. Following this 

 boundary northward the chert passes into black iron, and contains thin 

 sheets of White Porphyry from one foot to two feet in thickness. In the 

 abandoned workings just south of No. 2 shaft a winze was sunk 120 feet, 

 entirely through White Porphyry, which was finally abandoned on account 

 of great influx of water. 



At No 2 shaft the ore body was 17 feet thick, and lay immediately 

 beneath the Wash. About thirty feet north of this shaft the first White 

 Porphyry in place was found overlying the ore. North of this line the 

 ore horizon, which hitherto has been very flat, dips rapidly to the north, 

 the incline which follows it descending 20 feet in a distance of 50 feet. 

 From the foot of this incline run connecting drifts to the northern body, 

 which develop, on the ore horizon and immediately above the underlying 

 porphyry, masses of manganiferous iron and compact reddish chert, coated 

 frequently with crystals of pyrolusite. The chert which is developed in 

 the ore horizon, and which is one of the normal replacement products of 

 the Blue Limestone', though very similar, yet differs somewhat from the 

 concretions of chert found in the unaltered limestone, and which are very 

 commonly included in the White Porphyry immediately above the contact. 

 The latter is always compact and homogeneous, while the former readily 

 splits into angular fragments, and its joints .are frequently coated with deli- 

 cate crystals. 



The connecting drifts from the foot of the incline pass through this 

 barren vein material, or through the White Porphyry under it, and crossing 

 the Gray Porphyry dike, reach the northern ore body beyond it. 



