The stratigraphic terminology of the Pennsylvanian of southwestern Illinois is reviewed. The Boskydell sandstone lies above the Pounds sandstone ( = lower massive Makanda) but not above the Grindstaff sandstone, and therefore below the Willis coal. The Boskydell contains conspicuous amounts of small quartz pebbles and large quartz granules, a characteristic normally associated with the Caseyville group rather than with the Tradewater group. The Boskydell sandstone contains poorly preserved marine fossils which were deposited more or less in situ. The entire Boskydell sandstone probably exceeds 30 ft. in thickness; the actual geographic extent of the Boskydell is not known.