Previous uncertainty in the continuity of mapped moraines of central New York east of the Utica meridian resulted from the rugged topography and the complex interaction of the Mohawk and Ontario ice lobes. Till composition, fabric, stratigraphy, and drumlin morphology demonstrate that Valley Heads drift was deposited by a major readvance of the Ontario lobe after recession of the Mohawk lobe. This study names and describes a previously unrecognized moraine between Cassville and Cooperstown, New York. The moraine crosses several divides, permitting calculation of ice-front gradients, which are comparable to those of active, steady-state, temperate glaciers. Ice-slope considerations and topography suggest correlation of the Cassville-Cooperstown ice border with the Wagon Wheel Gap Substage in the Catskill Mountains.

Mapping the Cassville-Cooperstown moraine makes possible the tracing of older recessional positions of the ice sheet. Recession is inferred as uniform, with little local-valley control, suggesting an active retreating ice front rather than widespread stagnation. Although previous writers have suggested otherwise, ice recession was subparallel to the Terminal moraine in Pennsylvania and perpendicular to striations and to through valleys.

Regional correlations imply that deposition of the Cassville-Cooperstown moraine was simultaneous with the Rosendale readvance in the Wallkill Valley inferred at 14,800 radiocarbon yr B.P. Recession of the Mohawk lobe and readvance of the Ontario lobe to the Valley Heads moraine is suggested to be concurrent, resulting from initial isostatic rebound subsequent to deglaciation of the Adirondack dome.

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