Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/49

Rh the double basin at the river, occupying the valley of that name between the Seven Notch mountain on the north and Shriner’s mountain on the south, and carrying the Clinton rocks in its trough to within 14 miles of the county line.

8. The Jones mountain anticlinal may, in the same manner, be considered the westward prolongation of the river axis, splitting lengthwise into Shriner and Dull mountains, containing between them a small valley of No. III slates.

9. The Lewisburg synclinal, as the map coloring indicates, is the deepest trough in Union, as it contains north of Lewisburg a belt of No. VIII Marcellus slate and Hamilton sandstone 2 miles wide on the river, narrowing to a point about 3 miles west of Lewisburg. Here it is concentrically encircled by the Oriskany sandstone No. VII and the Lower Helderberg limestone No. VI of the Limestone Ridge, in a single simple synclinal fold, 1½ miles wide, on Buffalo creek. This is the Lackawanna basin of Northumberland.

Still further west a large area of the upper Salina lime shales and marls succeed, which create the fertile Buffalo valley; but while seemingly a wide smooth plane, its structure becomes more confused by the presence hereabouts of several small anticlinals and synclinals; whose growing strength as they are followed westward lead to the elevation of mountain rocks like those already described to the north, between which occur synclinal valleys of Clinton rocks. The chief of them are:

10. The Forrest Hill synclinal, first detected north of Mazeppa in the valley of Armstrong run, elevating the Bloomsburg shale at Forrest Hill, then the Clinton rocks further west and finally at the head of North Branch valley holding the sand rocks of No. IV of the Dull and Little Buffalo mountains.

11. The Little Buffalo mountain anticlinal, next south, first well seen west of Mazeppa in lower Salina and Clinton rocks, in time elevates its mountain sand-rock spur in Lewis township, and finally brings to daylight a narrow tongue of No. III slate along the Centre county line.