Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/55

Rh where it rises in the knob south of Middleburg, until it subsides again as it rose, below Jack’s creek on the Juniata.

4. The Shamokin synclinal enters Snyder county at Pine island, about 2 miles above Port Trevorton, holding the Catskill rocks in its trough for about 3 miles west of the river. Its dips are generally steeper than in the Northumberland basin, so that in Northumberland county the basin separates rapidly to finally admit of the coal measures at Trevorton and Mt. Carmel.

So on the west side of the river the basin shoals up and contracts. The Catskill rocks No. IX are succeeded by the Devonian No. VIII. The axial line passes through the southern part of Washington township to Mt. Pleasant Mill and Freemont in Perry, where only the Marcellus black slates are held in its trough, until at 2½ miles west of Freemont the Oriskany sandstone No. VII is brought to daylight, making a wall around the slate valley which is continued as a tightly compressed synclinal ridge of Lower Helderberg limestone No. VI, 2 miles long to a point north of Richfield. Beyond this the synclinal approaches more nearly to the base of the East Shade mountain, marked by a fertile valley of Clinton and Salina lime shales and slates.

5. The Slenderdale anticlinal axis of Juniata county is represented in Snyder immediately south of the Shamokin synclinal, carrying the upper Salina lime shales on its crest, north of Richfield, east to the line of Perry and West Perry townships. Here the Lower Heilderberg limestone and Oriskany sandstone in turn fold over the dying axis, the sandstone disappearing beneath a plain of Marcellus No. VIII black slate, just southwest of Freemont. The axis cannot be traced far east of this point.

All the southern part of Snyder county is composed of the different members of No. VIII, which along both forks of Mahantango creek, as well as along the river, show two subordinate anticlinals and synclinals of no great importance, and only serving to duplicate and spread the outcrops of these rocks.

6. The Tuscarora mountain anticlinal of Juniata county, after passing through Perry county, makes itself felt in the