Some 80 metres below the Beaumaris Peninsula, is a buried mountain range of Silurian rock. It was formed of sediments laid down some 400 million years ago and compressed into fold mountains. These were then rendered flat - worn away by erosion during the next 150 million years. In those times, individual continents as we know them today did not exist. They were all part of one landmass - the super-continent Pangaea. It began to break up and drift apart only about 180 million years ago. At first it separated into two parts - the northward drifting Laurasia and the more southerly mass called Gondwana. Australia was part of Gondwana, and even then the area which was to become Port Phillip Bay was part of a subsiding lowland situated near the edge of the drifting continent. Australia became isolated, and sea invaded the coastal lowlands. For a long time, rivers deposited gravel and sand on top of the Silurian rock to form what is known as the Fyansford formation. Fossil remains of shelly fauna can be found in these sediments, where they are seen at the surface near the area occupied by Keefer's Fishermans Wharf.
The Formation of Surface Rocks:
Sitting on top of the Fyansford formation are two layers of sedimentary rock that are visible around the Black Rock and Beaumaris coast. The bottom layer of the two (Black Rock Sandstone) is harder and darker in colour than the top layer (Red Bluff Sandstone), but geologically they appear to be closely related. About 12 million years ago, sea level fell slightly and the hinterland of Port Phillip Bay was uplifted. This rejuvenated streams flowing into the Bay, and they deposited about 15 metres of coarse, iron-rich sand on top of the Fyansford Formation. Shells and woody material became embedded in the sands, and appears in fossilised form in the rock of the shore platforms at Black Rock and Beaumaris.
Some 7 million years ago, a similar process of hinterland uplift and stream rejuvenation occurred, but this time the newly deposited sands were less rich in iron oxides. They formed a rock that is therefore softer than the Black Rock Sandstone. The new mass reached a depth of 24 metres, and is known as Red Bluff Sandstone. These layers were deposited on the sea floor at that time. Then there followed a period of uplift and gentle folding which brought them above sea level and created a low plateau of elevated land, part of which is the Beaumaris Peninsula. Wave erosion cut the sandstones back to form the cliffed coastline we know today. The folded rocks are seen in exposed and submerged nearshore reefs, and cliffed headlands where upfolds bring the harder Black Rock Sandstone above sea level. Sandy beaches formed in the intervening downfolds that bring the softer Red Bluff Sandstone below sea level.
The Black Rock Sandstone appears as the brown or dark brown strata forming the base of most cliffs, and all shore platforms and reefs. The softer Red Bluff Sandstone overlies it, which is often yellowish-orange in overall appearance. However, closer examination may reveal smaller segments of several other colours as well. Much of this colouration is probably due to the mineral glauconite. This is an iron bearing compound which, when oxidised forms iron oxides which are yellow, orange, red or brown in colour, and form a coating on the quartz grains. Colouration of this type is most notable in the Red Bluff Cliffs. Iron oxides are dissolved away in some places, leaving the sandstone grey or white, as in the cliffs at Black Rock Point.
Two million years ago the Earth’s climate became much colder and glaciers and ice sheets formed in polar and mountain regions. There were oscillations of climate, the colder glacial phases interspersed by warmer, drier periods, and during these drier times, the unconsolidated surface sands of the Beaumaris plateau were formed into parallel ridges by the prevailing north-westerly winds (see figure 2). Seasonal streams and swamps sometimes occupied the low corridors (swales) between the ridges. Beaumaris High School was built on the site of one such swamp, which extended across Balcombe Road to Balcombe Park Reserve. Though the swamp has long since been drained, the course of the seasonal stream with which the swamp was associated, is still marked by a line of River Red Gums at the rear of the School. It is the last stand in the local region of this once common wetland species.
Fish, Animals and People:
Migratory and free-ranging fish visit local coastal waters, but there are permanent populations of territorial fish such as Blennies and Zebra Fish. There are communities of invertebrate animals ranging from worms, sponges, seastars and sea urchins to anemones, crabs, molluscs and tunicates. They form an ecosystem at the base of which are the water plants, notably seaweeds, which provide food, protection and other services to the animals of the ecosystem. Seaweeds, in turn, require a firm substrate on which to attach themselves. This is provided by the upfolds of Black Rock Sandstone, which form the reefs and shore platforms of the area. Were it not for these upfolds, the nearshore waters surrounding the Beaumaris Peninsula would comprise a sandy and relatively lifeless desert.
The Bunurong Tribe of aborigines travelled as far south as Anderson's Inlet in South Gippsland. In their semi-nomadic wanderings along the coast, they collected such food as was available - in spring, swans' eggs from French Island in Westernport Bay, for example. It seems likely that the more westerly clans would have spent the warmer months on the Beaumaris Peninsula. Two factors suggest this. They spent considerable time fishing and collecting shellfish, and the preferred time for this would be in summer, as the Bay temperature falls to 8 degrees Celsius in winter. The second is that they placed considerable importance on the seepage-fed fresh water wells at the foot of the sea cliffs. At cooler times of the year, seasonal streams would have rendered such wells unimportant.
In a curious way, their shellfish eating habits also suggest that they appreciated the natural beauty of the Peninsula, in the same way that we do today. The location of two major cooking and eating spots (kitchen middens) are at Table Rock Point and Black Rock Point. These sites are by no means the only ones close to shellfish habitats, but may have been preferred because of the beauty of their sandstone structures, and the views they afford - both of the Bay and, as they prepared their evening meal, of the setting sun. Another advantage of these elevated sites was their exposure to sea winds, which would get the fires burning well as they cooked the shellfish.
Before the white invasion of their lands, a wide range of game was available to the aborigine. Some (koalas, possums, snakes and lizards) would have been a good deal easier to catch than others (kangaroos, wallabies, birds, etc.). In any event, game was not usually the main source of food for the aborigine. Most came from gathering by women and children. Apart from shellfish gathering, many coastal and inland plants offered a source of nourishment. Banksia flower spikes were soaked in water, and the nectar dissolved out to make a sweet drink; leaves of some plants are edible (such as Bower Spinach), fruits of others were eaten such as that of Pig-face. Some plants were uprooted for their tubers. It is worth noting that plants also provided a range of useful items - twine, basket material, clothing, canoes, weapons and tools, glues, medicines, fish poisons, fire sticks and fuel.
In some places, the topography has been noticeably modified. In the interest of safety, some coastal cliffs have been artificially shaped into gentler bluffs, whilst some beaches disappeared - the unintentional side effect of the construction of sea walls and a breakwater. However, the landforms of the coast generally retain their original character. Inland, the sand-ridge and swale formations are intact, though as we most often experience them - lined with asphalt or covered by buildings - they may be hard to recognise. They are far less modified in the golf country and on the Royal Melbourne and the Municipal Courses particularly, patches of native heath can still be seen. No widespread patches of woodland remain in the region, and swamps, along with most of their attendant vegetation, have been completely wiped out.
Despite these losses and modifications, the Peninsula retains something of its original character. Remnant patches of heathland have been carefully preserved in small reserves, whilst Beach Park is one of the less disturbed parts of the metropolitan coast. It may be that many of the people who came to live in the area, sense and appreciate the special qualities of its natural heritage. They attempt to perpetuate it by planting or retaining native species in their gardens, and elect representatives who will act in a like manner in public places. Local authorities, conservationists, teachers and many others work to retain a connection with the product of geological and biological evolution, regarding as precious, whatever part of it remains.
Now, the procedure to log the cache.........
For approval to log the cache, from the resources available to you at the original coordinates, please email me the following information
- A system of ancient river channels have been discovered out from the Red Bluff in Port Phillip Bay.
What scientific method was used to outline the ancient river channels?
- The channels are described as existing late in which geological era? Please highlight the spelling error in this name on the board
- Email your answers to me at email@example.com . This is important as it will go directly to my phone and I can respond immediately. Emails to my geocaching.com account could get lost in my watchlist emails which I don't look at as frequently.
- (optional) Your log would be enhanced if you include a photo of yourself with the Red Bluff in the background to accompany your found log. There are many times and angles from which to do this in order to make your photo unique.
I don't mind if you log a conditional find in order to preserve the order of your finds in your stats, but I will delete logs which are not confirmed as above within a week of the conditional log, in accordance with the rules for earthcaches..
I hope you enjoy your visit to this iconic symbol of Port Phillip and Melbourne.
I am fortunate enough to live only a few hundred metres away from this spot.
goes to Lemmykc, congratulations.