The features that became the Niagara Falls were created by the Wisconsin glaciation, about 10,000 years ago. The same forces also created the North American Great Lakes and the Niagara River. All were dug by a continental ice sheet that drove through the area like a giant bulldozer, deepening some river channels to make lakes and damming others with debris.[6] Scientists believe that there is an old valley, buried by glacial drift, at the approximate location of the present Welland Canal. When the ice melted, the upper Great Lakes emptied into the Niagara River, which followed the rearranged topography across the Niagara Escarpment. In time, the river cut a gorge through the north facing cliff or cuesta. The unusual rock formations did not erode evenly because of the interactions of three major rock formations.[citation needed] One rock formation was composed of erosion-resistant limestone and Lockport dolostone. That hard layer of stone eroded more slowly than underlying materials. The aerial photo clearly shows the hard caprock, the Lockport Formation (Middle Silurian), which underlies the rapids above the falls and approximately the upper third of the high gorge wall. Immediately below the hard-rock formation, comprising about two thirds of the cliff, lay a weaker, softer, sloping Rochester Formation (Lower Silurian). The formation was composed mainly of shale, though it has some thin limestone layers. It also contains ancient fossils. In time, the river eroded the soft layer that supported the hard layers, undercutting the hard cap rock. Eventually the process carved out the falls. Submerged in the river in the lower valley, hidden from view, is the Queenston Formation (Upper Ordovician), which is composed of shales and fine sandstones. All three formations were laid down in an ancient sea, and their differences of character derive from changing conditions within that sea. View of Niagara Falls, showing parts of Canada and the United StatesThe original Niagara Falls were near the sites of present-day Queenston, Ontario, and Lewiston, New York, but erosion of their crest has caused the waterfalls to retreat several miles southward. Just upstream from the Falls' current location, Goat Island splits the course of the Niagara River, resulting in the separation of the Canadian Horseshoe Falls to the west from the American and Bridal Veil Falls to the east. Although engineering has slowed erosion and recession in this century, the falls will eventually recede far enough to drain most of Lake Erie, the bottom of which is higher than the bottom of the falls. Engineers are working to reduce the rate of erosion to postpone this event as long as possible.

An inside panoramic view of the Georgian Bay cave.