Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/174

146 F³. portion of the township, is the only village and is not far distant from the Union county line.

The drainage is largely carried off through Penns creek and its small tributaries, some few small branches of Middle creek rising in the high plateau along the southern portion of the township and flowing southward through Franklin township to Middle creek, but hardly affecting the topography of Centre.

The structure is that of a simple synclinal, the general dip of the rocks being southward away from the Jack’s mountain anticlinal into the Northumberland basin, whose axis extends east and west through the Methodist and Zion churches, generally parallel to the southern border line of the township.

The rock series exposed extends from the red Medina sandstone along the summit of Jack’s mountain up to the Catskill red sandstone No. IX, which occupies the basin of the Northumberland synclinal for about 4 miles west of the Jackson-Middle Creek line before expiring by erosion at a point midway between the two churches just mentioned.

The Medina rocks No. IVb and No. IVc are first lifted to daylight along Penns creek, and rise rapidly westward in a long regular slope to form the crest and flanks of Jack’s mountain, Neither of these formations is well exposed in this township, although they affect the topography distinctly.

The lower Clinton shales create a strip of valley land along the south flank of the mountain, back and to the north of the Ore sandstone ridge with few exposures and dipping steeply to the southeast. At Centreville this dip is fully 60°, so that the overlying Ore sandstone and ore-measures outcrop high upon the mountain, practically on a level with the terrace of that ridge, so that the ore beds become difficult of access and would necessitate the driving of long cross-cuts to afford any length of stopes.

The Ore sandstone continues to remain comparatively shaly as it shows eastward along this side of the anticlinal in Union county, and west of Centreville the ore ridge merges to a great extent into the Jack’s mountain terrace.