Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/82

54 F³. by this means, no less than from the glistening white and lemon-yellow color of its sand.

In Juniata county the formation again deteriorates, and, where present at all, it is usually in the form of flint or chert rocks, in which condition it is unfit for glass purposes.

The Flintstone ridge before spoken of, in Snyder county, carries the same name here, and shows a zigzag course east of the Juniata, in obedience to the structural laws governing its exposure, from Richfield to Port Royal. Large accumulations of sand take place at the extremity of the canoe-shaped basins, where the two opposing dips meet, but the formation is not thick, averaging perhaps 40′ in this part of the district, with perhaps an equal thickness of sandy shale below it. This latter is both calcareous and siliceous; and usually quite hard, breaking into small square pieces, with sharp edges and quite as resisting to atmospheric influences as the more massive members of the formation.

On the south side of the main Tuscarora synclinal, along the foot of Turkey ridge, No. VII is scarcely perceptible. West of the Juniata two low Oriskany chert ridges flank the main valley all the way into Huntingdon county, their rocks the same but dipping toward each other, creating hills which are rarely farmed now but given up to the cultivation of peaches, to which their sandy soil seems very well adapted. The sandstone is here 20-25′ thick, the shale perhaps twice as thick. This formation is also exposed on the crest of the Tuscarora mountain anticlinal, at McKee’s Half Falls, in the extreme southeastern corner of the county.

Some little iron ore has been mined from the upper sandstone members in one or two places in Mifflin county, and in Juniata county and other points the Oriskany ridges are covered with a mass of siliceous hematite ore, which has never yet repaid the amount of money spent in its development, and is in fact worthless.

This formation has been given a deep blue tint on the map for the two-fold purpose of distinguishing it from