A thin black shale overlying the B-coal underclay (in the Middle Pennsylvanian post-Pottsville strata of the Bernice Basin) contains a compression flora composed of large, prostrate, unidirectionally oriented lycopod trunks and randomly oriented pteridosperm stems. This deposit is believed to have been formed by high-energy winds. -from Authors
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A Pennsylvanian-age terrestrial storm deposit: using plant fossils to characterize the history and process of sediment accumulation.