The Niagara Escarpment is the most prominent of several escarpments formed in the bedrock of southern Ontario. It is traceable from the Niagara River to northern Michigan, forming the spine of the Bruce Peninsula and Manitoulin and other islands in northern Lake Huron. It also extends into New York State and Wisconsin, roughly encircling the Michigan structural basin in the bedrock.
How was it formed?
The escarpment formed over millions of years through the differential erosion by weather and streams of rocks of different hardnesses. The Niagara Escarpment has a caprock of dolostone which is more resistant and overlies weaker, more easily eroded shale rocks. Through time the soft rocks weather and erode away by the action of streams. The gradual removal of the soft rocks undercuts the resistant caprock, leaving it standing as a cliff - the escarpment. The erosional process is most readily seen at Niagara Falls, where the river has speeded the process. The Niagara Escarpment is not formed by faulting. There is no displacement of the rock layers at the escarpment, as shown by study or rock exposures and drillholes. Additional resistant rock layers make more than one escarpment in some places. Also, in some places thick glacial deposits conceal the Niagara Escarpment, such as north of Georgetown, but it continues underground and reappears farther north.