Deposition of the complex sedimentary facies in the Allegheny basin exhibits a change in the dominant source of sediment influx from north to southeast through Pennsylvanian time. Lobate deltas entered eastern Ohio from both the rising Appalachian Mountains to the east and southeast and from the Canadian shield to the north. Confusion exists regarding the limits of the respective deltas. The present study is an attempt to define the limits of these sedimentary domains for a small portion of the basin in space and time. Samples of the upper Freeport (Upper Desmoinesian) and Mahoning (Lower Missourian) sandstones were collected along their western outcrop through eastern Ohio from Summit to Gallia Counties along a north-south transect. Thin sections were point-counted and a alyses of the data made to determine whether the individual samples had their source in the high-grade metamorphic and igneous crystalline basement of the Canadian shield, or among the sedimentary and low-grade metamorphic rocks of the Appalachians. Determination of the source of the samples allows delineation of the boundary between respective delta lobes.

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