A sequence of rocks of Late Devonian, Mississippian, and Pennsylvania!! age, more than 11,000 feet thick, is exposed in an area of about 27 square miles in west-central Schuylkill County, Pa. These Paleozoic rocks are overlain at many localities by a varying thickness of unconsolidated, sediments of Quaternary age. The entire sequence of rocks accumulated in a continental environment. The upper part of the Catskill formation of Late Devonian age, 500 to 1,000 feet thick, crops out in the northwestern part of the report area. This unit consists of red, brown, and gray sandstone, siltstone, and shale. The 'Catskill formation is overlain unconformably by 1,050 to 1,100 feet of strata assigned to the Pocono formation of Mississippian age. The Pocono consists largely of gray to brown quartz conglomerate, conglomeratic quartzose sandstone, and quartzose sandstone. The Mauch Chunk formation of Mississippian age, 2,500 to 6,000 feet thick, succeeds the Pocono with apparent conformity. It consists largely of red sandstone, siltstone, and shale, but contains some interbedded gray conglomerate, sandstone, siltstone, and shale in its basal and upper parts. The overlying Pottsville formation of Early Pennsylvanian age consists of about 1,100 feet of predominantly gray quartz conglomerate, conglomeratic quartzose sandstone, quartzose sandstone, subgraywacke, siltstone, shale, and a few coal beds ; its basal beds intertongue with the red beds of the Mauch Chunk. The Pottsville is divided into the Tumbling Run, Schuylkill, and Sharp Mountain members, in ascending order. Post-Pottsville rocks of later Pennsylvanian age rest with apparent conformity on the Pottsville formation. They consist of about 2,150 feet of light-to dark-gray quartz conglomerate, conglomeratic quartzose sandstone, quartzose sandstone, subgraywacke, siltstone, shale, and many coal beds. The report area, which is in the Southern anthracite field, is on the north limb of the arcuate and completely deformed Minersville synclinorium. The limb of the synclinorium is folded into many doubly plunging anticlines and synclines and is broken by thrust, tear, and bedding faults. The trend of the folds ranges from N. 65°E. to N. 85°E. The fault system within the Pennsylvanian rocks is dominated by a series of low-angle folded thrust faults that are truncated by later high-angle thrust and tear faults and paralleled by bedding faults. The 181 00 CO