The Middle Devonian Marcellus Shale is one of the premier gas shale plays of North America in terms of total gas resource, extent, production rates, and economic potential. The organic-rich shale of the Marcellus was deposited in a foreland basin setting that was sediment starved and allowed for accumulation and preservation of the organic material. The Marcellus Shale Formation is positioned in the lower portion of the Hamilton Group, which is bounded above by the Middle Devonian Tully Limestone and below by the Lower Devonian Onondaga Limestone. The Upper and Lower Marcellus Shale are divided by the Cherry Valley/Purcell Limestone.