BREE INSTITUTE OF ¡SGLENGE 
MINERALOGY OF THE NEWARK GROUP IN PENNSYLVANIA 
changing its color from red to gray. The presence of other dikes nearby is 
suggested by the fragments in the fields, but they are not exposed in place. 
For some 700 feet further north the sediments are of the normal red 
sandy shale character, but the dip gradually increases to 50°. Then evidence 
of alteration begins to appear; the shale is first, to a distance of 125 feet, strongly 
indurated, without change in color. The succeeding zone of “ variegated red 
shale and sandstone,” 
about ten feet wide, is evidently the result of the same 
degree of metamorphism affecting layers of different composition. For 50 
feet further the shale is light gray and very hard, a sort of hornfels, and then 
comes the solid trap. The actual contact is somewhat obscured by weather- 
ing, but the base of the trap is quite conformable with the bedding of the shale. 
In the immediate vicinity of the contact the trap is rather fine grained, but 
gradually increases in coarseness upwards, the maximum of 1 inch crystals of 
feldspar and pyroxene being reached about 50 feet below the upper surface. 
The exposure is 900 feet in width, corresponding to a thickness of 800 feet; and 
on the east side of the creek it ceases abruptly at a small transverse stream, 
north of which gray altered shale fragments are abundantly present in the soil. 
The west bank of the creek is here quite steep, however, and exposures of trap 
continue over 100 feet beyond the first sign of shale on the east side. A few 
boulders of finer grained material appear at the immediate contact, within five 
feet of greatly indurated gray shale dipping about 60° north 40° east. The 
gray color persists to a thickness of over 20 feet, but the exposures are not 
sufficient to permit of following the changes closely, as could be done below the 
sheet. The normal red color is, however, soon resumed, and continues for 
half a mile northwards along the creek. 
Just below the dam of Althouse's mill-pond igneous rock again appears, 
but this time without warning, the soil up to the solid trap exposure remaining 
bright red, and, on the west bank, above the gate to the race, fresh sandy red 
shale outcropping on the hillside within two feet of the trap. The boundary 
between the igneous and sedimentary rocks is here a beautifully sharp one, 
an abrupt change from red soil derived from the shale to the yellow soil produced 
by the weathering of the iron-bearing silicates in the trap being traceable across 
the fields for a considerable distance. 
On the east side of the creek the hill rises suddenly from the meadow 
below and the contact is obscured by boulders; but about 200 feet back along 
the base of the hill a rather peculiar relation appears. A small quarry has been 
