Phase 3 of the Champlain Sea is defined as the interval that
followed the retreat of the Laurentide ice from the Saint-
Narcisse Moraine. Events included are the retreat of ice from
major valleys in the Laurentian Highlands, invasion of these by
the Champlain Sea and regression of the Champlain Sea from its
entire basin. In the lower Saint-maurice Valley, post-Saint-
Narcisse retreat of an active ice-front is recorded by the
Cossetteville parallel ridges. Transverse ridges of the middle
Saint-Maurice Valley and Lac du Missionnaire indicate the
presence of an active ice-front in these valleys. Elsewhere,
ice-frontal constructions and raised outwash trains were formed
at the mouth of valleys, e.g. the proglacial delta perched at an
altitude of 200m, at the mouth of Lac Mekinac. The Champlain Sea
extended into the Laurentian Highlands in the form of brackish
or freshwater bodies considered as paramarine basins (Occhietti,
1977) At the close of Phase #, considerable shoaling had already
taken place and waters in th