The axis crosses the river at Mexico, where the two outcrops of Oriskany sandstone, enclosing the slate valley, are scarcely one-half mile apart. A mile west of the river they are even closer, but there gradually begin to diverge, the valley meanwhile filling up with a greater thickness of slate. The axis is well seen at the first bend in Tuscarora creek, with dips of 40°, and again just where the road from McCoysville south crosses the creek, with dips of 25° south and 10° north. The trough line then bends a little south, passes through the high ridge south of Willow run, and keeps about midway between the two sandstone and limestone ridges flanking the valley all the way to Huntingdon county.
East of Mexico the trough likewise widens and deepens, crossing Delaware run north of Thompsontown, swerving to the southeast slightly to become indistinct along Dutchman’s run.
16. The Tuscarora mountain anticlinal forms the south wall of this basin from Huntingdon county to the Juniata river gap above Millerstown. It is really monoclinal in Juniata county, one-half of the roll being in Perry county. Its course is broken by the synclinal Liberty valley in Tuscarora township, from which the mountain rocks of No. IV rise both ways. It is in every respect like the other mountain ranges of this district.
