The youngest rocks are the top layer which was formed around 410 million years ago, during the Middle Silurian period. The older rocks at the water line were formed around 420 million years ago, during the Upper Ordovician period.
Dolomite is a hard rock formed when limestone is infused with magnesium.
The Escarpment also contains sandstone and shale. The shale was formed from accumulated sediment at the bottom of a shallow muddy inland sea. It began to form around 430 million years ago, when a warm shallow sea centred around the Michigan peninsula. Over millions of years, sediment plus lime-rich organic material from ancient coral reefs was deposited here. The escarpment represents older rock pushed to the surface, where it was subject to erosion and other weathering processes.