TRANSACTIONS OF WAGNER 
MINERALOGY OF THE NEWARK GROUP IN PENNSYLVANIA 
opened here, exposing the underlying shale, dipping 50° north 20° east. West- 
ward this extends below the surface of the ground, the trap overlying it in a 
perfectly conformable manner, but on the cast the trap breaks across the beds 
of the shale, and is exposed to a distance of five feet, apparently as a sort of dike. 
The soil of the meadow effectually conceals the further extension of this dike, 
so that it can not be definitely proved that it connects with the intrusive sheet 
below, although it is quite possible that such is the case. 
This shale is slightly metamorphosed, its normal red color being changed 
to dull brown, but the intense alteration, such as is exhibited below the 
southern sheet, is entirely lacking. The trap is welded to the shale, and although 
weathering has caused considerable disintegration, specimens can be secured 
showing this contact. The trap is extremely compact, dense, and fine grained 
throughout the greater part of this exposure, but about two feet above the 
contact on the shale it contains occasional amygdules filled with quartz, cylin- 
drical in outline, and averaging one-half inch in diameter by three inches long. 
These are no doubt to be interpreted as gas or steam cavities lengthened by the 
flow of the viscous lava; the direction of lengthening is north 25° west. 
A series of trial excavations for road metal has been made along the road 
north of this point, so that the trap is well exposed throughout its entire thick- 
ness of 500 feet. The fine grained character shown at the lower contact persists 
upwards for over a hundred feet, with occasional slightly porphyritic arcas. 
Then minute cavities begin to appear, and these increase in number gradually, 
until at the top the rock is highly vesicular. The cavities are in part filled 
with various secondary minerals, chiefly calcite, prehnite and datolite, the last 
being confined to a narrow layer about 350 feet below the top; to these attention 
will be further directed below. 
The extremely porous character of the upper part of the trap mass having 
rendered it particularly susceptible to weathering, the contact with the overlying 
shale is nowhere exposed. In the road bank, however, there occurs a broken- 
up, scoriaceous material, impregnated with calcareous red mud, along with frag- 
ments of red shale which do not show the slightest sign of metamorphism. And 
red shales, with occasional beds of conglomerate and sandstone, continue to 
be exposed along the creek to the boundary of the Newark half a mile to the north. 
There are two possible ways in which sheets of igneous rock interstratified 
with sedimentary rocks may be produced. In one type, known as extrusive, 
the molten lava has been poured out over the surface of the depositing sediments, 
