Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/74

46 F³. beds and is essentially a ridge-maker, whose soil is mostly barren and unproductive and very little cleared anywhere in the district.

The Genesee rocks, (VII e,) largely a series of dark blue, brown and black shale, weathering yellow, are essentially valley-makers, everywhere following the base of the Chemung ridges, and sharply distinguished from those rocks by the totally different topography produced. They are about 300′ thick in Snyder county.

The Hamilton proper, (VIII c,) on both sides of the Shade mountain anticlinal, carries about 1000′ of slate and brownish shale on top, which assist in widening the Genesee slate valleys; but the lower part, 1000′ thick, is much more massive, containing several beds of sandstone, which create a second line of ridges separated from the higher Chemung ridges by the Genesee and Hamilton valleys. Prof. I. C. White in Report G7, p. 79, gives a very interesting section of the entire series, measured along the Northern Central railroad below Selinsgrove Junction. He shows the lower part of the Hamilton above mentioned to consist of:

The Marcellus black slate, (VIIIb) the base of the Hamilton group, is a valley-maker, being readily eroded and decomposed. It is a dark black fissile slate, breaking in small, thin irregular pieces, and yielding a somewhat gray clay soil. Thickness about 300′. Beneath it Prof. White finds, along the railroad where the measures are well exposed for measurement in a bluff:—(a) Selinsgrove lower limestone, a hard light gray impure rock, in thin layers, interstratified with gray shale 65′ thick. (b) Selinsgrove shale, light gray impure limestone at top, 140′ thick. This would make the Marcellus slate division, therefore, about 500′ thick.

The different members could not be as well seen on the Snyder county side of the river as in Northumberland