Melbourne geology
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A Brief History of Melbourne Geology
References
A Brief History of Melbourne Geology
During its geological history much of the land of the Melbourne Basin has at several stages been an underwater seabed. It was uplifted, twisted and plunged under sea level many times as a result of global and localized geological change.
The Silurian sand and mudstone, common through out Victoria, consists of layers of sandy and clay deposits from its previous underwater and aboveground life. These layers have been hardened over time and pressure, some dating back as far as 450 million years.
The fossils typical of Melbourne's Silurian rock are often sea dwelling creatures, such as Monograptolites, Brachiopods, Starfish (Petraster), Cystiods (Henicocystis) and Trilobites (Trimerus).
In more recent geological times there was a period of volcanic activity in the north and west of Victoria, lasting somewhere between 5 and 15 thousand years and only ending about 4000 years ago.
Much of Melbourne's northern grassland areas lie above Basalt Plains, a product of the extensive volcanic activity. The common basalt rock, bluestone, which can be found thorugh out the streets and buildings of Melbourne, was mined from the many quaries located throughout Victoria.
During this period Melbourne's inland water systems were altered spectacularly. Molten lava flowed into, at times filling, the existing creek and riverbeds. The current meandering paths of many of Melbourne's rivers are a direct consequence of these Newer Volcanics, as Geologists describe them.
The Yarra River displays wonderful examples of the effects of the Newer Volcanics. The lava blocked the water's course, so that it became dammed in the Doncaster and Templestowe areas, before it was able to find a new path. The basalt, formed by the cooled lava, is considerably harder and stronger than sandstone - through which the water eventually cut its way again to Port Phillip Bay.
Eventually Silurian cliffs were formed, like sections through geological time. Many such cliffs are typical of the Yarra River today, at places such as Dights Falls and Studley Park, where one can see the synclines and anticlines, which describe the uplifts, drops and twists of the land as it was transformed.
There still exist many ancestral paths of Melbourne's rivers and creeks.
References
:: GW Cochrane, GW Quick and D Spencer-Jones. Introducing Victorian Geology,
:: Ian Clarke, Barry Cook. Victorian Geology Excursion Guide, Australian Academy of Science 1988 ISBN 0 85847 143 4
:: JG Douglas and J A Ferguson. Geology of Victoria, GSA
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