Widespread occurrences of stratified silt and clay have been found under the surface sands on the crest of the Oak Ridges Moraine between Stouffville and Pontypool, Ontario. It is suggested that the most likely explanation for the submergence of that part of the moraine is that the Lake Ontario ice lobe was still overriding the Niagara Escarpment at the time, holding standing water in the area between the southern and northern ice lobes and the escarpment. A stream channel over the escarpment, extending from northeast of Cheltenham to Acton and beyond, may have served as the outlet. This sill is high enough to have held water over the above-mentioned silts and clays. It is of interest that this outlet channel led eventually to glacial Lake Whittlesey, indicating a correlation.