Reconnaissance of eastern Ontario regions lying between the late-glacial positions of Lake Iroquois and the Champlain Sea provides new information on ice-flow patterns as represented by striae and other streamline phenomena. This is related to the distribution of ice-marginal deposits and to structurally controlled topography. Two ice lobes, Madawaska Highland lobe and Ottawa – Lake Ontario lobe, are identified, and the Oak Ridges interlobate moraine system is extended. Discussion of apparent sequences of events allows for a new working hypothesis, including the concept of a calving bay in Ottawa Valley, for the development of the Champlain Sea, and for the timing of the drainage of Lake Iroquois. It reconciles radiocarbon dates previously thought to be anomalous.