Detailed investigation and mapping of the Pennsylvanian rocks in Oklahoma is sufficiently advanced to permit fairly definite tracing of formations north of the Arbuckle Mountains to the type section in Kansas. Interruption of outcrops in southern Oklahoma makes correlation of the Pennsylvanian section of the Ardmore basin and of north-central Texas dependent on paleontologic evidence, lithologic characters, sequence of deposits, and relation to structure. The significant facts concerning each of these criteria are discussed briefly, and a tentative correlation of the Pennsylvanian beds from Texas to Kansas is offered. Evidence is cited pointing to at least two important

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orogenic epochs during Pennsylvanian time in southern Oklahoma, the first of Pottsville (post-Morrow) age and the second in the late middle (post-Kansas City) part of the period.