Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/80

52 F³. It is also found encircling the Buffalo valley synclinal at Lewisburg, though nowhere well exposed, and consisting of a mass of yellowish-brown sand lying on the flank of the limestone ridge.

It is again enclosed in the Mifflinburg synclinal, occurring in three slender detached patches on the crest of the long limestone ridge south of Mifflinburg. Its sand has no commercial value here, being discolored and shaly. The formation cannot be over 25′ or 30′ thick; and the underlying flint shales do not seem to occur at all.

In Snyder county the formation is more widely distributed but, nearly everywhere, a chert, and of no economical importance. It occurs on both sides of the main Northumberland synclinal from the Susquehanna to the Juniata line; but in many places along the north side of the valley it is wanting, and always indistinct and very thin. It is slightly more distinct on the south side of this synclinal, and sometimes shows a good, but thin, bed of sand; but it is practically worthless for glass purposes.

In Flinstone ridge, extending from the river below Selinsgrove towards Freeburg and Freemont, its chert beds form the crest and give the name to this conspicuous hill. The thickness of the formation could not be well determined; but it falls within 40′; and is everywhere a hard chert.

In Mifflin county the formation shows its best development, especially from the neighborhood of Lewistown west to Mt. Union. It is variable here too, both in thickness and character, but augments gradually towards the south west. The Oriskany sandstone is about 50′ thick in Decatur township, being well exposed on the flanks of the two subordinate anticlinals which jut out into the Devonian slate valley from the Kishacoquilias creek.

In the ridge north of Lewistown the same formation is 110′ thick, but it is not particularly massive, showing a rather soft sandstone 40′ thick, between layers of shaly sandstone, and the Oriskany shales beneath it are put at