146 
AMERICAN GEOLOGY - . 
groundless. When the Hall mine was first opened, it enlarged 
to eight feet. Afterwards it diminished rapidly to less than four 
feet. Fig. 33, is a section of this part of the vein. It was 
eight feet w T ide at a, a, and when I examined it in 1837, it was 
pinched out to four feet. At this stage of the working it was 
a question what would become of the vein. On pursuing it 
farther and into the constricted part, it began to widen again, 
and has proved to he one of the most valuable mines in the 
Moriah mineral district. It has been worked to the depth of a 
hundred feet. The vein appears inexhaustible. A transverse sec¬ 
tion of this district, about one hundred yards, furnished at least 
three parallel veins. The annexed section was made in 1837, 
fig. 34, a, a, veins, b, b, gneiss. All of these have been proved 
Fig. 34. 
to the depth of seventy or eighty feet, the ore increasing in 
richness with the depth. They have been traced about one and 
a half miles. Their line of bearing is northeast and southwest, 
and they dip with the plane of lamination of the gneiss in which 
they are inclosed, and half a mile west of the Sandford mine, 
they have been extensively worked, and yield a pure black 
granular oxide. Phosphate of lime is not present in the three 
parallel veins, although in the immediate neighborhood of the 
Sandford mine which is so rich in it. 
The veins of magnetic iron contain ore whose quantities dif¬ 
fer materially from each other. No two veins, however near, 
supply the same kinds of ore. A good example and one in 
point, are the well known veins in the Clintonville mining dis- 
