Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/279

Rh and normal synclinal holding the upper Salina shales, crossing the stream near the northern limits of Yeagertown; from which point successively lower strata rise (going up stream) on dips of 55°–58°; until at the entrance to the gap the white Medina sand-rock No. IVe complete the section.

South of Lewistown the same section which occurs between Yeagertown and the gap is duplicated, only with reverse dips, the rocks in this part of the field inclining towards the north and northwest at angles varying from 80° to 50°.

The Shade mountain, which is of anticlinal structure, ends at the Juniata river, which after passing its end just below Jack’s creek, turns almost at right-angles eastward and flows through the narrow synclinal valley of lower Clinton rocks between Shade mountain and Blue Ridge known as “the Narrows.”

There are no good exposures of the Medina sandstone in Shade mountain, although a vast quantity of loose bowlders of this rock flank its sides and give an especially wild and rugged aspect to the “Narrows.”

Jacks mountain is of similar rock, and the character and thickness of its three members as exposed in Logan gap have already been described in Brown township.

Lewistown itself is situated upon the upper Salina shale and marl, which is so calcareous at this point as to readily account for the great fertility of the soil here. The first ridge north of the town is composed of the Lewistown limestone No. VI, which (with the exception of one small anticlinal roll about 2 miles east of Lewistown, causing a slight reversal in dip and an interruption in the course of its outcrop) spreads directly eastward in a prominent ridge just north of the Lewistown and Sunbury railroad into Decatur township. The crest and north flank of this ridge is everywhere composed of the Oriskany sandstone and shale, which, with the underlying limestone at Lewistown, dips from 40° to 45° to the northwest. Both of these formations are well exposed on the Milroy pike near the toll-house, and are succeeded northwards by a band of Marcellus black slate with a similar dip.