A study of fusulinids in upper beds of the Gaptank Formation indicates that the Uddenites Zone is early Wolfcampian in age. Near the western end of the Glass Mountains, beds containing early Wolfcampian fusulinids were overridden by part of the Dugout Creek thrust sheet. Evidently Marathon disturbance thrusting extended from Pennsylvanian into early Permian time. Lithology and fossils suggest that the conglomerate bed in the lower part of the type section of the Wolfcamp Formation, about Neva in age, represents detritus shed from the front of the sheet at or near the end of thrusting.

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