As the Laurentide ice sheet retreated from this area glacial lakes formed along the ice margin. Two of the largest proglacial lakes in this area were Lake Algonquin (north of the Oak Ridges Moraine) and Lake Iroquois (within the Lake Ontario basin). The Iroquois shoreline is recognizable by the truncated drumlins (1) and slightly subdued topography below this elevation. The drumlins in this image are a continuation of the Peterborough Drumlin field which extends beneath the Oak Ridges Moraine.

Further Reading

Anderson, T.W. and Lewis, C.F.M. 1985: Postglacial water-level history of the Great Lake Ontario basin; in Karrow, P.F. and Calkin, P.E., (eds.), Quaternary Evolution of the Great Lakes Geological Association of Canada, Special Paper 30, 213-253.

Coakley, J.P. and Karrow, P.F. 1994: Reconstruction of post-Iroquois shoreline evolution in western Lake Ontario; Canadian Journal of Earth Sciences, 31, 1618-1629.