"Acton Peninsula Limestone Outcrops are a significant group which extends 80m-100m along the eastern shore of Acton Peninsula. The age of the limestone is Late Silurian (approximately 425 million years) and it contains sparsely distributed fragmentary macro fossils of corals and shells. Very little limestone is now exposed in the area. The Acton Peninsula Limestone Outcrop is the most accessible and continuous exposure of the limestone which induced Europeans to give the area the name Limestone Plains, now the site of the National Capital.
Associated with the Acton Peninsula Limestone Outcrops are quartz rich gravels from the Tertiary (between 5 and 65 million years old). These gravels sit directly on top of the limestone and in some places have formed potholes that indicate that the Molonglo River once flowed over this site. The ancient water level is about 25m above the height that the river was before the formation of Lake Burley Griffin." Source: Australian Heritage Database
