. Bulletin of the Geological Society of America. Geology. NON-MARINE PROGRESSIVE OVERLAP 633 ghenies, the formation is 1,107 feet thick and consists at the base of 227 feet of Greenbrier limestone resting directly on the Pocono, followed by 800 feet of shales, mostly red. Southward, in Pendleton county, West Virginia, the Greenbrier limestone at the base is 325 to 400 feet thick, and is followed by gray and brown sandstones and shales and red shales (Canaan shales), with a thickness of 1,250 feet. These shales, however, are in all probability only partly non-marine. The Mauch Chunk thus seems
. Bulletin of the Geological Society of America. Geology. NON-MARINE PROGRESSIVE OVERLAP 633 ghenies, the formation is 1,107 feet thick and consists at the base of 227 feet of Greenbrier limestone resting directly on the Pocono, followed by 800 feet of shales, mostly red. Southward, in Pendleton county, West Virginia, the Greenbrier limestone at the base is 325 to 400 feet thick, and is followed by gray and brown sandstones and shales and red shales (Canaan shales), with a thickness of 1,250 feet. These shales, however, are in all probability only partly non-marine. The Mauch Chunk thus seems to present two periods of non-marine fan-building separated by a period of partial subsidence. Non-marine (fluviatile) sedimentation appears to have been continuous in eastern Pennsylvania throughout. In both periods the greatest accumulation of non-marine sedimentation was in the east, and the members overlapped westward and northward. A diagrammatic section will make this Figure 15.—Relation of the Upper and the Lower Mauch Chunk and the Greenbrier. The upper Mauch Chunk fan represents the recovery of the land after the Greenbrier subsidence. With this recovery corresponds the presence of coarser sands in the upper Mauch Chunk in the eastern region, where non-marine sedimentation was uninterrupted. That the land was low and streams sluggish is indicated by the fact that the surfaces of the beds are marked by ripple-marks, sun-cracks, rain-drop impressions, and foot- prints of vertebrates—all signs of floodplain deposits. The fossils of the Greenbrier in southern Pennsylvania and Maryland correspond to those of the Maxville of Ohio. The Maxville is separated from the Logan by an interval of erosion, which may correspond to early Mauch Chunk sedimentation in the east; for the beginning of a new fan on an older one indicates either an increased supply of detritus or a period of elevation. The fineness of the lower Mauch Chunk is, perhaps, more in harmony with the the
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