Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/78

50 F³. broader valleys. All the ridges however die out westward as the basin shoals up, confining the No. VIII rocks to a narrow tongue on both sides of the Juniata, mainly filled up with the Marcellus rocks.

Turkey ridge, limiting the district and the county on the south, is composed mainly of the Hamilton sandstone. It rises perhaps 150′ above the valley, and runs for about 11 miles, decreasing in height towards the Juniata. Southwest of the Juniata the lower members of the formation are contained in a regular synclinal valley about half a mile wide, gradually widening to the southwest to receive higher strata along its center.

At Honey Grove the valley is nearly 3 miles wide, and about here the Chemung rocks first make their appearance, creating the typical narrow straight ridges due to the hard sandstone strata composing them.

The Marcellus limestone is exposed at various places in the Tuscarora valley, notably at Peru Mills, where the top layer is a good limestone 2′ thick, underlaid by an impure greenish calcareous rock, and a considerable thickness of lime-shales, probably 100′ thick.

Along the Huntingdon county line the whole group is about 3300′ thick. The Marcellus division at the bottom is largely black slate with some gray and buff calcareous shales and thin argillaceous limestone, and grading upwards into more or less massive white sandstone strata separated by dark shales, the whole being 600′ or 700′ thick. The Hamilton and Genesee are largely olive and bluish-black slates, with some brown layers and thin sandstones, 800′. The Portage rocks are not so easily distinguished as on the Juniata, but are quite massive along the flanks of the Chemung ridges, and generally of a smooth texture and dark in color, and about 1000′ thick. The Chemung rocks on top and along the center of the valley are composed of thin but very hard gray sandstone, breaking into long flat layers and show a decided cleavage. There is some shale also, reddish-brown in color, and fissile, the whole producing a lean soil, so that the ridges in western Juniata are very little cleared for farming purposes.