Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/106

78 F³. Between the Tuscarora synclinal (Nos. VIII, VII and VI) and the Tuscarora mountain, the entire Salina and Clinton series are exposed. The Ore sandstone and Iron sandstone outcropingoutcropping [sic] with steep dips, hug the base of the mountain pretty closely, making merely terraces as far west as Liberty Valley. But in Tuscarora and Lack townships the dips are not over 30°–40°, so that these rocks, especially the Ore sandstone, here about 20′ thick and massive, make distinct ridges out in the valley, with the Clinton upper olive and red shales and the Salina rocks creating a broad flat between the outer (Ore sandstone) ridge and the Lewistown ridge No. VI.

The upper Salina marls and lime shales fill a narrow but well defined synclinal basin, characterized by a series of sink-holes, from the Juniata in Turbett township, west to the Spruce Hill township line.

More detailed references to the character of the individual members of the Salina and Clinton series will be given in the chapter on Township Geology.

This formation can be conveniently divided into three members, IVc, upper or white Medina sandstone; IVb, lower or red Medina sandstone, and, IVa, Oneida gray conglomerate and sandstone. Economically considered, these rocks are of comparatively small importance in the district. They contain no ores or minerals of value, and while portions of the formation should make good building stone and in some few instances possibly a fair sand-rock for glass-making, they have nowhere been so used as yet.

It has been already explained how all the mountains of the district are composed of one or the other of these divisions of No. IV, and with comparatively slight variation as to thickness and coarseness of constitution, they usually present similar characteristics, whether in the Buffalo mountain, the Seven mountains, Jack’s mountain