Niagara Escarpment

On these photos you can get a better idea what Niagara Escarpment is. It is composed of the Lockport geological formation of Silurian age, and is similar to the Onondaga geological formation, which runs parallel to it and just to the south, through western New York and southern Ontario. The escarpment is most famous as the cliff over which the Niagara River plunges at Niagara Falls, for which it is named.

The Niagara Escarpment is the most prominent of several escarpments formed in the bedrock of the Great Lakes basin. From its easternmost point near Watertown, New York, the escarpment shapes in part the individual basins and landforms of Lakes Ontario, Huron and Michigan. In Rochester, New York, there are three waterfalls over the escarpment where the Genesee River flows through the city. The escarpment thence runs westward to the Niagara River forming a deep gorge north of Niagara Falls, which itself cascades over the escarpment. In southern Ontario it spans the Niagara Peninsula, closely following the Lake Ontario shore through the cities of St. Catharines, Hamilton and Dundas, where it takes a sharp turn north in the town of Milton toward Georgian Bay. It then follows the Georgian Bay shore northwestwards to form the spine of the Bruce Peninsula and Manitoulin Island, as well as several smaller islands located in northern Lake Huron where it turns westwards into the Upper Peninsula of northern Michigan, south of Sault Ste. Marie. It then extends southwards into Wisconsin following the Door Peninsula through the Bayshore Blufflands and then more inland from the western coast of Lake Michigan and Milwaukee, ending northwest of Chicago near the Wisconsin-Illinois border.

That is what Wikipedia has to say about it.