Glacial Lake Whittlesey is related to the glacial advance during the Port Huron Stadial, approximately 13 000 radiocarbon years BP. This episode has previously been thought to be represented, in the eastern end of the Lake Erie basin, by the Paris and Galt Moraines and the deposition of the Wentworth Till in southern Ontario.However, the location of Whittlesey shoreline features suggests that this lake existed during the subsequent advance which deposited the Halton Till. A 'Halton' ice-contact delta, at Summit, Ontario, coincides with the Lake Whittlesey water plane curve constructed from 72 data points around Lakes Huron and Erie.It is suggested, therefore, that the glacial ice advance represented by the Halton Till, based on its relationship to Lake Whittlesey, has an age of about 13 000 radiocarbon years BP (Port Huron Stadial) and that the Wentworth Till (Paris and Galt Moraines) is of Port Bruce Stadial age.