Beginning with the Marcellus slate, the measures occur in the following descending order:—
a. Hydraulic cement (probably Upper Helderberg), very hard and compact.
b. Blue clay, about 6 inches thick.
c. Paint-ore, varying from 6 inches to 6 feet in thickness.
d. Yellow clay, 6 feet thick.
e. Oriskany sandstone, forming the crest and southern side of the ridge.
East of the Rutherford shaft the sandstone forms the top-rock of the bed. This is due to an overthrow occurring between the Rutherford tunnel and shaft.
The paint-bed is not continuous throughout its extent. It is faulted at several places; sometimes it is pinched out to a few inches and again increases in width to 6 feet. A short distance south of Bowman’s there is a fault striking; north-east in the Marcellus slate, which has produced a throw of about 200 feet. The measures dip from 10° to 90°. The dip at the Rutherford shaft is about 79° south, whereas at the tunnel it is 45° north. The ore is bluish-gray, resembling limestone, and is very hard and compact. The bed is of a lighter tint, however, in the upper than in the lower part, and this is probably due to its containing more hydraulic cement in the upper strata. The paint-ore contains partings of clay and slate at various places.
At the Rutherford shaft there are fine bands of ore, alternating with clay and slate, as follows—Sandstone (hanging-wall), clay, ore, slate, ore, clay, ore, clay, ore, slate, ore, cement, slate (foot-wall). These partings, however, are not continuous, but pinch out, leaving the ore without the admixture of clay and slate. Near the outcrop the bed becomes brown hematite, due to the leaching out of the lime and to complete oxidation. Occasionally, streaks of hematite are interleaved with the paint-ore. In driving up the breasts, towards the outcrop, the ore is found at the top in rounded, partially oxidised and weathered masses, called “bombshells,” covered with iron oxide and surrounded by a bluish clay. In large pieces the ore shows a decided cleavage.
The method used in mining is a variation of panel-work. Nearly the same system of working is employed by all of the companies who have developed their mines either by means of tunnels or shafts. Tunnels are preferred whenever equally convenient, because they involve no expenses for pumping and hoisting machinery, fuel, repairs to machinery, &c.