suburb. Geology The southern part of Acton has a complicated arrangement of sediments that include the Pittman Formation greywacke and the black-coloured Acton Shale Member from the Ordovician age. Then from the Silurian age there is mudstone, State Circle Shale, and Camp Hill Sandstone. Some limestone is found near the National Museum of Australia. Calcareous shales from the Canberra Formation are overlain by Quaternary alluvium on the north. This rock is the limestone of the original title of Canberra, "Limestone Plains". Tertiary-age pebbly gravels are left from when the Molonglo river was at a higher level. Notes and references Suburbs of Canberra