Silurian Period sediments laid down 430 million years ago were metamorphosed underground into a gneiss 360-415 million years ago, and intruded by molten rock which cooled slowly, creating the park's exposed metamorphic gray rocks with dikes of harder, white igneous rock. Underground heat and pressure tortured and folded the rock layers into the striking patterns that are now pounded and polished by the sea and rough weather.