Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/62

34 F³. creek at Logan; the Lewistown section, 2½ miles further west; and the section at McVeytown, besides numerous local sections of the subordinate rock waves between Lewistown and Mt. Union.

7. The Lewistown synclinal valley, viewed as a whole, is deeper geologically at either end than in the center, and therefore contains at its ends in Mifflin county a much greater thickness of the No. VIII slates and sandstones than in the central portion. Moreover, several of the tightly compressed anticlinals and synclinals which occur between McVeytown and Lewistown die away east and west, making one broad valley of the Lower Devonian measures.

The seeming irregularity of the central portion of the belt is reduced to perfect order and clearness once that this key to the structure has been applied. The structural features of the valley have largely increased its commercial wealth; for had the basin been simply a normal one there would have been only a single series of outcrops on each side of the valley, the ores, limestone and sandstone of the north half towards Jack’s mountain descending far beneath the Juniata river to appear but once again along the south half of the valley against the Blue Ridge. Instead of that the outcrops these ores and limestones, whose extraction has added so much to the wealth of the county in the past, are repeated several times, producing the zigzag appearance of color on the map, and presenting the iron ores, limestone and glass-sand to more advantageous and cheaper development. The local features of the district will be described later in the Township Geology.

8. The East Shade mountain anticlinal has already been partly described, passing through the mountain of that name and its slate valley of No. III, and touching the Juniata at the mouth of Jack’s creek here in Mifflin county. The plane of this axis is like a bow, subsiding towards both ends from the Snyder county line, until on the Juniata the Medina crest of the mountain sinks completely beneath a plain of the lower Clinton rocks, which show on the west and south side of the river.