The limestones near the base of the Stratford formation of the Pontotoc series have been traced around the west end of the Arbuckle Mountains, and then southeast to a point near Ardmore. This mapping was done before George D. Morgan's report on the "Geology of the Stonewall Quadrangle, Oklahoma" was published; and since the top, rather than the bottom, of the limestone series was followed, the line shown on the map does not coincide with one of Morgan's formation boundaries. The base of the Asher formation, which is next above the Pontotoc series, was also traced around the mountains and found to overlap the shale in the upper part of the Stratford formation. At the west end of the mountains the Asher formation rests directly on the limestones in the lower part of the Str tford formation, which are in contact with the upturned edges of the Ordovician limestones; all lower members of the Pontotoc series are absent. The conglomerates near Berwyn, formerly called Franks, are assigned to the Pontotoc series, and a correlation made across the mountains by J. T. Richards on the basis of some concentric-ringed pebbles which have been banded by algae. It is suggested that the uncertain boundary between the Permian and Pennsylvanian be placed at the base of the Asher formation.