Moruya Tonalite (age 379 my)
Moruya Granite is the commercial name for stone that was quarried during the 1920’s near Moruya on the New South Wales south coast and transported by steamer to Sydney Harbour for the construction of the pylons of the Sydney Harbour Bridge. At least one barge used in the transport is now half submerged on the banks of the north side of the Moruya River. Hundreds of tourists now climb up the Harbour Bridge pylons every day to get a magnificent view of Sydney Harbour from the top of the bridge steel arches.
The geological name of the rock is Moruya Tonalite, a rock unit within the Moruya Suite of rocks comprising six north-south-trending elongate granite plutons at the extreme eastern side of the Bega Batholith.
These rocks were emplaced at a few kilometres depth within the Earth’s crust during the Middle to Late Devonian geological period. Subsequent erosion has exposed them at the surface.
Photo: Moruya tonalite being quarried in 1926. The rocks were used to construct the iconic Martin Place Cenotaph and the pylons of Sydney Harbour Bridge.
Image courtesy NSW State Records.