Geologic evidence indicates that the Niagara River began to cut its gorge (Niagara Gorge) about 11,000 years ago as the Laurentide Ice Sheet retreated from the area. The ice started at the Niagara Escarpment shown in figure 5.9 and receded north to form the basin of Lake Ontario. The Niagara Gorge started at the Niagara Escarpment and retreated south to its present location. Based on this geochronology and the length of Niagara Gorge, calculate the average rate of falls retreat in cm/year.

Queenston Shale Brown Wrirpool Sandstone Escarpment Nagara Narth Lockport Dolostore (Green) Niagara Gorge 2 kn Goat is Niagara Fals Nagara River FIGURE 5.9 Geology of the Niagara Gorge Region. The Niagara River flows from Lake Erie north to Lake Ontario and forms the border between the United States and Canada. Niagara Falis is lecated on the Niagara River at the head of Niagara Gorge, about half way between the two lakes.