The deglaciation of the study area started around 13,500-13,000 years B.P. and was distinguished by the existence of an Appalachian ice mass that produced glacial erosion marks, three morainic segments, numerous eskers, and various accumulations of ice-contact stratified drift. Field data allow for the reconstruction of an active phase of this Appalachian ice, which was quickly followed by a stagnating phase. The separation of the northward-flowing Appalachian ice from the main southeastward-flowing Laurentide Ice Sheet was produced by an upstream progression of a calving bay in the St. Lawrence River Valley. This progression stopped in the valley bottleneck near Québec City, where the zone of separation shifted inland onto the present south shore of the St. Lawrence River. From this point the separation of the Appalachian ice took place on land and was not controlled by the calving bay. Near this zone of separation, the Laurentide ice produced the Highland Front Moraine. It was not until the retreat of the Laurentide ice front from the Highland Front Moraine position that marine water could invade the St. Lawrence Lowlands. A tentative chronology of events is presented.