Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/344

316 F³. to a dip of 60°. These are the Chemung light colored shales and thin sandstones, and show in an exposure here about 100′ thick.

North of Oriental the dip is reversed to 10° northwest in dark gray to black Genessee slates, which continue south to the store and show along the creek below the G. M. on a 15° northwest dip.

Mahantango Creek flows east for some distance in a valley eroded out of these slates and the upper Hamilton shales until a little over a mile from the river, at the entrance of a small branch stream from the north, the Hamilton gray sandstone is exposed in the gap in a bed 20′ thick, dipping northwest 35°. It makes, as usual, a high sharp crested ridge and in passing through the gap along the main creek the same gray sandstone with some few shale beds is exposed repeatedly, with a total thickness of about 150′. South of this ridge and between it and the Georgetown limestone anticlinal the creek flows through a wide belt of lower Hamilton and Marcellus shales and slates, all showing gentle northwest dips. These rocks are superbly exposed just north of Arnold’s G. & S. M. upon a dip of N. 15° W. 40°, extending for 150 yards along the creek in an almost uninterrupted outcrop of blue-gray sandstone, thin bedded brown shales and the Marcellus black slate.

The Oriskany sandstone making the short ridge running west of Mahantango P. O. everywhere shows a thin bed of chert rock producing a sandy gravel soil, containing a great number of flint bowlders. This rock flanks both sides of this ridge, the crest of which is composed of an elevated area of Lewistown limestone nowhere very well exposed.

From the river at Weiser’s store and grist mill, west through the Turkey valley and the southern part of Susquehanna township, the exposures are everywhere meagre. At the forks of the road near the river there is a small outcrop of gray sandstone apparently dipping 70° to the southeast, which would indicate a rather tightly folded synclinal of Marcellus and Hamilton measures.

North of the Strawser church, about 4 miles west from the river, the Genessee shales are exposed in the north lip