The highlands of west-central Maine, including the Longfellow and Boundary Mountains, were overridden at least twice, probably three times, by a continental ice sheet during Wisconsinan time. These episodes are indicated by at least five widely separated exposures displaying two-drift sequences composed of thick lodgment tills separated by glaciolacustrine and fluvial sediment. Radiocarbon dates on an intertill pollen- and wood-bearing deposit at New Sharon, Maine, record a major nonglacial interval that ended more than 52,000 B.P.
The last ice sheet, actively building end moraines along the Maine coast 13,500 yr ago, had thinned, separated, stagnated, and dissipated over the Longfellow and Boundary Mountains at least by 12,500 B.P. Contemporaneous stagnation, throughout and southeast of the mountains, is evidenced by the distribution and volume of ice-contact stratified drift. Coupled with this is the lack of evidence for receding active ice margins associated with either the Laurentide Ice Sheet or a late-glacial locally centered ice cap suggested by some workers. In addition, the highest cirques in the study area, floored at approximately 930 m, reveal no evidence of reactivation during and subsequent to the dissipation of the last ice sheet.