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The middle Pennsylvanian Allegheny Formation, which crops out in the Appalachian Plateau of West Virginia, represents nonmarine equivalents of deltaic marine-brackish-nonmarine strata northwestward in Pennsylvania and Ohio. In West Virginia, the Allegheny is some 300 feet thick and consists mainly of sandstone, shale, coal, and seatrock units, none of which displays any great degree of lateral continuity. Sandstone units, which in cross section are about 60 feet thick and roughly 5 miles wide, are arranged in an en echelon manner within an anastomosing plexus of shale, coal, and seatrock. Sandstones presumably represent fluvial bar sands whereas shale, coal, and seatrock suggest various backswamp environments. The en echelon arrangement of bar sand units probably arises from major lateral shifting of channels into adjoining topographically lower backswamps. Differences in proportional abundance and dimension of channel and backswamp elements from southern to northern West Virginia suggest a transition from an alluviated upper deltaic plain to a partially inundated lower deltaic plain.

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