Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/139

Rh bank of Penns creek, where it forms a low ridge in the north leg of the Northumberland synclinal of Snyder county. A limited area of the Marcellus black slates No. VIII is exposed in the loop of Penns creek a short distance west of the mouth of Sweitzer run.

The Jack’s Mountain anticlinal and the Mifflinburg synclinal are the two most important and striking structural features of the township.

The former, after rising on the east from the Susquehanna river, succeeds in elevating a strip of Medina rocks on its crest for nearly 5 miles in length in Shamokin mountain, which is a virtual eastern extension of the main Jack’s mountain. The axis continues to rise for a distance of about 8 miles west of the river to a point opposite New Berlin, where, partly in this township and partly in Buffalo township, it has exposed the red Medina rocks on its crest for about 1¼ miles, the ridge being about 600′ at this point above the level of Penns creek.

Westward from this point the anticlinal descends rapidly, until in about 2 miles, along Sweitzer run, the flexure is spanned at water level by the lower Clinton shales south of Battletown, with dips of 10° and 15° north and south.

From this point the axis again increases in strength westward and at the same time increases the north and south dips along Penns creek to 35° and 60° respectively; and just before reaching the Penns Creek Narrows it elevates the white Medina sandstone No. IVc, 200′ above creek level, and to even greater elevations on the west side of the creek, where the mountain is fully 600′ high.

The Medina rocks are well exposed on the north dip of the anticlinal along Penns creek, 80′–100′ thick, on a northwest dip of 35°.

The Iron sandstone of the lower Clinton measures, occurring about 500′ geologically above the Medina sandstone, is also well exposed further west towards the Lewis township line on the Hartleton road, near David Baertges’ sawmill, where it shows 20′ or 30′ of a hard bluish-gray rock, weathering red at the outcrop, dipping N. 22° W. 30°.

The Ore sandstone makes a distinct ridge further north,