182 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
NEW JERSEY DEPOSITS. 
The New Jersey copper ores occur in the eastern part of the State. 
They were worked more or less continuously from colonial days until 
some thirty years ago. Several properties have recently been reopened, 
and in one instance extensive development work has been carried on. 
The ores all occur at or near the contact between the shales and sand- 
stones of the Newark group (the red sandstone series of Triassic age), 
and the trap rocks. These traps all occur tilted at gentle angles, 
commonly conformable with the shale beds. Orange Mountain, and 
the second and third mountains back of it, collectively known as the 
Watchung Mountains, are formed by these trap sheets, the sand- 
stones forming the intervening valleys and foot slopes. These traps 
are lava flows contemporaneous in age with the shales, while all the 
other trap sheets of the State have proved to be intruded bodies. 
The copper ores occur above and below these trap rocks. 
In Watchung or First Mountain, back of Plainfield, and the contin- 
uation of the mountain south and west to Boundbrook and beyond, 
the trap is underlain by a stratum of altered shale that is almost con- 
tinuously copper bearing. This constitutes the most important cop- 
per deposit of the State, one that has been worked at fully 30 dif- 
ferent places in former years. The most important development has 
been near Somerville, at the American copper mine. The workings 
at this place follow down the ore stratum for a distance of 1,350 feet 
from the surface, the bed being inclined at an angle of about 10°, 
dipping into the mountain. The ore occurs in a well-defined bed, 16 
inches to 3 feet thick, lying immediately beneath the trap rock, the 
latter rock being also occasionally ore bearing for a few inches next 
the contact. 
For a distance of nearly 15 miles along the mountain front this con- 
tact stratum has p roved copper bearing. The ores consist of the red 
oxide of copper with green carbonate and silicate, sheets of native 
copper, and rarely peacock copper and glance. In the American 
mine the workings pass through the upper oxidized part of the bed, 
characterized by the ores just mentioned, into a lower zone in which 
they are wanting and in which native copper occurs in small masses 
scattered through the ore bed, together with a very little finely dis- 
seminated glance, associated with calcite. The native copper occurs 
in grains and irregular nodules in bunches of white or grajash-colored 
ore irregularly scattered through the purple rock. As no average 
sampling was attempted, it may be stated that the systematic sam- 
pling of the company's representative is said to have yielded 2^ per 
cent copper, a figure which if sustained by mill work will permit of 
the profitable working of the property. 
At Arlington and many of the other localities of the State the ore 
consists of oxide, carbonate, and glance, filling cracks and crevices in 
