Unconformity

Peter Hoffman points out the boundary between the Devonian Rondout Formation (above) and the Ordovician Normanskill (below). 1987 fieldtrip led by Anderson and Goodwin, upstate New York.

Breaking Rock

Actually, this rock broke back in the Devonian Period. The white stuff is gypsum, which filled the spaces among the pieces of shattered rock, forming a new fabric and creating an altered rock that is called breccia. The light gray layer underneath is much older. It is Ordovician, and the surface in between represents an immense amount of time. This kind of surface is called an unconformity.