Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/398

370 F³. the public road and the mountain, but the limestones are everywhere eroded; the sink-holes are absent and the basin is occupied by the upper Salina lime shales which prevent underground drainage and compel the mountain runs to pass over them to the Tuscarora creek.

The upper Salina rocks flank the Sink-Hole valley on either side in Turbett township and are best exposed on the north side away from the mountain drift, where they form a wide belt with dips of from 50°—70°, S. E. The succeeding anticlinal to the north between the Sink-Hole and Tuscarora valley synclinal is largely composed of the Bloomsburg red shales or the lower Salina rocks, showing more conspicuously in Turbett than in Spruce Hill township.

In the former township on the road from the Tuscarora water station to Port Royal, via Hertzler’s store, the upper Salina rocks are seen east of the brick school house, dipping 50° N. W. and 70° S. E., making a subordinate roll south of the main axis. To the north of the school, the Salina shales outcrop with variegated beds, but with comparatively little lime, to the road leading down to Blue Spring hollow. Here, at Jacobs’ place, some red beds occur, but are almost immediately succeeded by the upper Salina lime shales on northwest dips of 40°, flanking the South Limestone ridge.

The Lewistown limestone making this ridge spreads out on either side of the road forks at the head of the gap, followed by a band of No. VII chert, 100′± wide, and finally the Marcellus black slate on a 50° N. W. dip. A fine spring, giving the name to the ravine, emerges from the first (Hamilton ?) sandstone layer in No. VIII which dips about 30° N. W.

There is an excellent exposure of the No. VIII rocks through this gap, the synclinal holding some grey and drab shales with 20° dips, and the Marcellus limestone several feet thick near the bottom of the series north of the school. A thin sandstone, some 12′ thick, occurs in conjunction with with it, as at Lewistown, immediately above the lowest black slate. Its sand is sharp and largely discolored by iron.