Stratigraphic and paleontologic studies of the Pottsville and Allegheny groups [Pennsylvanian] of western Pennsylvania have resulted in the establishment of 12 environmental, faunal zones, some of which have proved useful in regional correlation and paleographic interpretations. Marine and restricted marine fossils, mainly Chonetes, Mesolobus, Marginifera, Lingula, Dunbarella, and Aviculopecten occur in dark-gray shales above the upper Mercer, lower Clarion, upper Clarion, Scrubgrass, lower and middle Kittanning coals. Fresh-water fossils, mainly estherids and Carbonicola are found in shales above the upper Kittanning, and lower and upper Freeport coals, and ostracods and small gastropods are found in the limestones below these coals. The most rapid faunal variation in all marine beds takes place in a general N.-S. direction. The marine fossils disappear to the N. and E. in the upper Mercer and lower Clarion shales, whereas they disappear to the NW. and SE. in the other beds.