Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/413

Rh The geological section of rocks is more extensive than elsewhere in Juniata county, from the fact that the Black Log axis elevates the top or Trenton layers of the Siluro-Cambrian limestones for about 2½ miles east of the Huntingdon county line along Black creek. The central portion of the township contains representatives of the Chemung rocks in the Tuscarora synclinal, so that the entire series between No. II and the top of No. VIII are here exposed.

The structure of this portion of the district has become greatly simplified by the expiration of the subordinate axis, which modify the topography and geology of the county in the vicinity of the Juniata river.

The Black Log valley anticlinal, on the north, the Tuscarora mountain monoclinal on the south, and the broad Tuscarora synclinal in the center are the only well marked flexures. As has been already stated, the first axis carries, for 2½ miles east of Huntingd onHuntingdon [sic] county line, a narrow wedge-shaped area of limestone on its crest, beyond which the entire valley of Black creek and the inside flanks of the two bounding mountain walls—Black Log and Shade mountains—are occupied by the Hudson River slates No. III.

The Black Log mountain of Oneida sandstone IVa, is a comparatively low ridge, forming a terrace on the south flank of the Medina crest, which is largely in Mifflin county. It is, however, coarsely conglomeritic, exhibiting along its strike a series of pulpit rocks, or dome-shaped outcrops, whose rocks dip northwest 40°–50°. The slates on its south flank are decidedly brown in color and are very readily eroded, thus presenting but few good outcrops.

Along the main valley road these rocks show all the way west to beyond the valley church, where they dip 60° S. E. A short distance beyond this point, on C. Gluck’s farm, a small limestone quarry has been opened on the south side of the creek, showing a few feet of limestone, dipping 35° S. E. into Shade mountain. This is No. II limestone which occupies so large an area in the Kishacoquillas valley and is the only place in Juniata county where it is exposed. West along the creek it is pretty generally covered with a