Prior to about 1963 it was generally accepted that northern New England and adjacent Canada were progressively deglaciated from southeast to northwest during Late Pleistocene time. R. Chalmers and E. Antevs thought differently, but their views were not seriously considered, although their models were basically correct as we understand the deglaciation pattern today. Since about 1963 abundant evidence has accumulated that demonstrates that the Laurentide Ice Sheet was partitioned by a marine calving embayment that advanced up the St. Lawrence Lowland to the Ottawa area at least by 12,800 years B.P. This event left ice sheet remnants over much of Maine, southeastern Quebec, and probably in New Brunswick and western New England as well. Continuing research is needed to delineate the details of the final deglaciation in southeastern Quebec and Maine. Data presently available suggests that the Longfellow, White, and Boundary Mountains emerged as nunataks as early as 15,000 years ago, separating the ice sheet to the north and south. The Frontier Moraine, located on the divide between Quebec and Maine, formed at that time. Subsequently, other moraines formed as the margin of the ice sheet receded northwestward into the St. Lawrence Lowland of Quebec.

Several glacial geologists working in Maritime Canada have developed a view of maximum late Wisconsin glaciation in which the Gulf of St. Lawrence and the Gulf of Maine were substantially ice-free, and ice calving into these embayments came from local ice domes, except for Laurentide ice calving into the Gulf of St. Lawrence along the Laurentide Scarp of Quebec. In contrast, most glacial geologists working in New England believe that Laurentide ice overrode all of New England and terminated as marine ice streams in the Gulf of St. Lawrence and the Gulf of Maine, and as terrestrial ice lobes in the Hudson River valley, the Connecticut River valley, and Great South Channel between Nantucket Shoals and Georges Bank. The view of New England glacial geologists is supported by numerous radiocarbon dates. Glaciological models of ice dynamics along an ice-sheet margin consisting of local ice domes, ice streams, ice lobes, ice shelves, and calving bays have been applied to the Maritime Canada/New England region. These models show that the viewpoint of glacial geologists in Maritime Canada is compatible with conditions during deglaciation, but that the viewpoint of glacial geologists in New England is compatible with conditions during the late Wisconsin maximum. The undated ice margin north of the Gulf of Maine favored by Maritime Canadians cannot coexist with the dated ice margin south of the Gulf of Maine mapped by New Englanders. The ice divide between a Laurentide ice dome in Noveau Quebec or Hudson Bay and a local ice dome in the northern Appalachians must have had a saddle over the St. Lawrence River valley. A saddle is incompatible with the late Wisconsin glacial geology, but is consistent with the glacial features formed during retreat.