Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/48

20 F³. 4. The Nittany mountain anticlinal, reaching the river a little over a mile below the last described synclinal, and keeping a nearly parallel course westward, lifts first the Ore sandstone and then the Medina white sandstone No. IV of the mountain, about 5 miles from the river; then in turn the lower Medina and Oneida, until the increasing strength of the axis is sufficient to part asunder the opposing walls of the mountain and admit of an enclosed valley of Hudson river slate No. III along the upper White Deer creek, and extending 4 miles long to the Centre county line.

5. The New Columbia synclinal, a trough whose axial line crosses the Susquehanna about a mile north of New Columbia, and being somewhat deeper than the White Deer Mills basin, contains a greater thickness of the upper Salina shales and marls, and does not elevate the Bloomsburg shale along its axis until at 6½ miles from the river. From here westward its rise is more rapid, so that before reaching the Centre county line it holds in its trough a synclinal ridge, Sand mountain, 4 miles long, composed of upper Medina sandstone, and occupying the valley of Spruce run.

6. Buffalo mountain anticlinal, touching the river a little south of New Columbia with comparatively flat dips, elevates the Ore sandstone in 1½ miles, with opposing dips of 40°, and in 5½ miles more brings up the Medina sandstone in the Buffalo mountain spur. This mountain bears a close analogy to Nittany mountain on the north, but, like it, its anticlinal axis going westward gradually forces its walls apart to admit of still lower rocks, until they finally enclose a slate valley of No. III nearly 3 miles long in Union, known as the Brush Valley Narrows in Centre.

South of Buffalo mountain the structure becomes slightly more complicated. At the river opposite Milton there is a narrow synclinal and anticlinal roll in the rocks within a mile of each other in the upper and lower Salina rocks, making long narrow tongues of the Bloomsburg red shale, as shown on the map, extending for some 6 or 8 miles from the river.

7. The Rapid run synclinal is the western extension of