The Lerderderg River rises below the Blackwood Ranges, part of the Great Dividing Range, in the Lerderderg State Forest, near the locality of Blackwood. The river flows generally south by east in a highly meandering course, joined by two minor tributaries, before reaching its confluence with the Werribee River within the Melton Reservoir, southeast of Bacchus Marsh. The river descends approximately 383 metres (1,257 ft) over its 40 kilometres (25 mi) course.
A diversion in the river's course, called the Lerderderg River diversion tunnel, located approximately 25 kilometres (16 mi) upriver from Bacchus Marsh, was constructed between 1855 and 1870. The tunnel was driven through a mountain spur in a horseshoe bend, diverting the river, and allowing the exposed river bed to be sluiced for alluvial gold.
The river is known for the Lerderderg Gorge Picnic Ground, camping, bushwalking, and fishing. In earlier days, gold was mined in the upper reaches, and some of the old mines (considered dangerous to enter) can be seen as you travel along the sluice on the east bank, which previously fed into those mines. The water has slowed down to a trickle for the past few years because of a severe drought, but there are still a few popular swimming spots along the river.
The geology of this area is diverse with a terrain resulting from three main groups of processes: volcanism, faulting and changes in sea level. These processes have created many features that make the region geologically significant including glacial material, deep gorges resulting from faulting, and lava flows and eruption points from volcanic activity.
Roughly 400-500 million years ago, the sea covered the area, allowing sand and mud to be deposited. After the sea withdrew, uplifting occurred, forming north-south running mountain ranges. This was followed by a long period of erosion. Approximately 250 million years ago, glaciers formed and as they moved over the land they exposed large granitic rocks. Rubble was deposited in the valleys and conglomerates and sandstone were deposited in the lakes and rivers that were created as the glaciers melted. These are some of the earliest glacial deposits known to exist in the world, adding to the geological significance of the Bacchus Marsh area.
Following movements of the Rowsley Fault approximately 1-2 million years ago, deep gorges formed along the Werribee River, Lerderderg River and Parwan Creek. The youngest geological materials are alluvial and colluvial fan deposits and confined floodplain deposits. Alluvial terraces then developed in the valleys of the Werribee and Lerderderg Rivers.
Feldspar
Sandstone is a clastic sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust.
Feldspars are a group of rock-forming tectosilicate minerals that make up as much as 60% of the Earth's crust. They crystallize from magma as veins in both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock.
Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as a filler and extender in paint, plastics, and rubber. In glassmaking, alumina from feldspar improves product hardness, durability, and resistance to chemical corrosion. In ceramics, the alkalis in feldspar (calcium oxide, potassium oxide, and sodium oxide) act as a flux, lowering the melting temperature of a mixture. Fluxes melt at an early stage in the firing process, forming a glassy matrix that bonds the other components of the system together.
There is a short drive between the listed coordinates and WP2. The idea of this Earth Cache is for you to be able to discover 2 different parts of this wonderful river. At the listed coordinates for Q1 & Q2, please be careful on the bank. It can be slippery. Please take your time.
Questions
Q1 At the marked coordinates, describe the river bank here on your right.
Q2 At the marked coordinates, look at the layers here. Estimate the size of the layers and how many can you count.
Q3 At WP2 describe the rock here along the rivers edge.
Q4 At WP2, what direction does the rock 'lines' look to be running at the rivers edge
Once you complete the EarthCache requirements you can post your find without delay, as per the EarthCache guidelines. You will also need to verify your find by sending me a message and provide your answers to the questions.
For a link to my profile, click here - Na'wal
Thanks for visiting this Earth Cache. Hope you enjoy the location.
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References ~ growwest.com.au, Wikipedia, geology.com