Before the dinosaurs roamed the earth and long before the Atlantic Ocean existed, large mountain chains lined what is today the East Coast. Once the mountains were formed however, the on going process of erosion began. Large Boulders, cobbles, pebbles and sand were worn away and washed into mountain rivers and streams. The water ways emptied into what is now the Narragansett Bay Basin. The sediments were deposited as the currents of the rivers and streams subsided.
Sedimentary rock is formed from layers of sediments piled on top of each other.
Millions of years of tectonic activity transformed the sediments into sedimentary rock. The conglomerate of boulders, cobbles, pebbles and sand from the eroding mountains helped to make the Purgatory Formation, sometimes called Puddingstone. Hanging Rock is part of this formation. Copyright 1999, The Norman Bird Sanctuary.