The Pottsville formation of Pennsylvanian age has been divided into three lithologic units in the Southern anthracite field as a result of detailed mapping and stratigraphic studies. It is redescribed, and member status is proposed for the three lithologic units which are here named, from the base up, the Tumbling Run member, Schuylkill member, and Sharp Mountain member. The three members are composed largely of pebble and cobble conglomerate, fine conglomerate, conglomeratic sandstone, and sandstone, with subordinate quantities of shale, siltstone, and coal. They have been mapped in detail throughout much of the central and western parts of the Southern anthracite field and have been traced by reconnaissance stratigraphic studies throughout the rest of the field. The mem ers have also been tentatively correlated into the central and eastern parts of the Western Middle anthracite field and the Eastern Middle anthracite field. The upper member has been tentatively correlated into the Northern anthracite field.

The type section along the eastern side of the Pennsylvania Railroad cut through the water gap south of Pottsville is now partly obscured, and the writers propose to designate as a reference section the complete exposure of the Pottsville formation that is present about 150 feet farther east in a present-day road cut on the east side of U. S. Highway 122.