 Geologically, the oldest rocks in the area date back to the Cambrian period 500 million years ago, with volcanic activity occurring in the Devonian period 350 million years ago.In prehistoric times water covered much of the lowlands that are now Geelong, with the Barwon River estuary located at Belmont Common, the course of the river being changed when Mount Moriac erupted and lava was sent eastwards towards Geelong.To the east of the city are the Bellarine Hills and the undulating plains of the Bellarine Peninsula.