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.