The purpose of this paper is to investigate the sedimentology and paleogeography of the Mississippian Mauch Chunk sandstones in south-central and western Pennsylvania. The thin-section, heavy-mineral, and size analyses form the core of the study. The sandstones comprise two groups: subgraywacke, forming the dominant group, and protoquartzite. The subgraywacke beds are considered to have been deposited by a river system on a fluvial and prograding deltaic plain; the dominant current direction, based on paleocurrent studies, was from east to west, indicating an eastern source composed of sedimentary clastics and a metamorphic complex. The protoquartzite beds were deposited in a nearshore marine environment during the early phase of the Mauch Chunk sedimentation; the source ock of the protoquartzite was composed of mature and multicycled sediments, and was north and northwest of the study area.

An isopachous and lithofacies map indicates that, in cross section, the Mauch Chunk is wedge-shaped and thins westward. The westward thinning of the terrigenous clastics is accompanied by an increase in the thickness of marine carbonates.

The sedimentary model presented for the Mauch Chunk Formation is that of a molasse basin, which is an elongate miogeosynclinal basin in which the terrigenous deposits thicken toward the source and thin seaward. The model is similar to those for the Juniata-Tuscarora, the Catskill, the Pocono, and the Pottsville molasse deposits of the central Appalachians.