The Niagara Escarpment extends over 600 km in Ontario from the Niagara Peninsula in the south, northward through the Bruce Peninsula, to Manitoulin Island. The Niagara Escarpment is a prominent physical feature of the Hamilton region and is locally referred to as the “Mountain”. It was formed 500 – 400 million years ago when sediments from the eroding Taconic Mountains were deposited in warm tropical oceans (known as the Michigan Basin) that covered the Great Lakes Basin and Southern Ontario. These sediments (sand, silt, clay) were buried and lithified into a variety of sedimentary rocks. Coarse sediments such as sand formed sandstones while finer material lithified into shales. Coral reefs were also present in the warm tropical oceans and over time resulted in the formation of limestone and dolostone.
Each rock unit dips gently towards the center of the Michigan basin. This dip is important to the formation of the Niagara Escarpment as it exposes older, less-resistant layers (such as shale) to erosion which then undercuts the more resistant dolostone cap rock. The Niagara Escarpment has been subjected to erosion over the past several million years.
The Niagara Escarpment was dramatically altered by glacial and fluvial erosion during the last 2.5 million years (Quaternary Period). Approximately 2 million years ago, the Escarpment was covered with an ice sheet ~2 km thick. The glacial advance shaped the landscape and in particular formed the Dundas Valley.
As the glaciers retreated (~ 25 to 13 Ka) glacial sediments (such as tills and moraines) were deposited on top of the Escarpment. Lake Iroquois formed (~13 Ka) in the basin currently occupied by Lake Ontario and subsequently drained ~12.2 Ka. Sandy sediments that underlie most of Westdale area in Hamilton and the high ridge of land that separates Cootes Paradise from Hamilton Harbour are features from ancient Lake Iroquois.
Glacial meltwaters also carved through the Escarpment to form the Niagara River and Niagara Falls. Landslides and slumps caused the escarpment to recede further over the last 10 Ka (Holocene Epoch) and many steep-sided valleys and ravines were cut into the edge of escarpment by rivers.
Geology of the Niagara Escarpment
The Niagara Escarpment is made up of hard, resistant dolostone ‘cap rocks’ (such as the Lockport Formation) that overlie softer, more easily eroded shales and sandstones of the Rochester, Thorold and Grimsby formations. The resistant dolostone units form prominent ledges, whereas the softer shales are covered by surface deposits or vegetation. The Niagara Escarpment is slowly migrating westward as the ‘cap rock’ progressively collapses due to undercutting of softer shales beneath.
The bedrock succession of the Niagara Escarpment is shown in this cross-sectional profile. Photos are from the exposure located at Rock Chapel, Hamilton. [Rock Chapel photos by Alan Sawula]