Whipstick Gully
This earthcache brings you to the largest quarry in Whipstick Gully. Now a popular abseiling wall, this quarry gives you a good look at the geological structire of Warrandyte. The quarries were worked in the 1940s and 1950s to provide stone for local buildings.
Whipstick Gully is part of the Warrandyte Goldfields, home to The Victory Mine (see waypoint). The Victory Mine was Warrandyte's most successful mining operation and contains the district’s most intact and visible remains of historic quartz.
The area consists of Silurian Rocks, principally sandstones and shales with sandstones of varying degrees of coarseness. The shales are perhaps the most predominant. Throughout wide areas they are thick-bedded and massively jointed, as well as extremely rubbly. Bands of sandstone are sparsely interbedded with them. Mica (generally muscovite) is extremely common in both the shales and sandstones, but in the latter rocks the flakes are larger, and therefore more noticeable. Many of the shaly rocks are when undecomposed, moderately tough, but on exposure they soon soften and break up.
How did these rocks form?
The Silurian Period, which in geologic time is the third period of the Paleozoic Era, began 443.8 million years ago and ended 419.2 million years ago, extending from the close of the Ordovician Period to the beginning of the Devonian Period. Australia was part of the Godwana continent, which was centered over the south pole and spanned Australia, Antarctica, India, Arabia, Africa, and South America. The flooded margin of eastern Australia had a more-varied seafloor topography than the other shallow seas because of the extensive volcanism occurring there during Silurian time, but it shared many of the same faunal elements because of its tropical latitude.
Nowhere on Earth do landscapes stay the same. Plants, animals, the weather, earth movements and gravity are breaking down the land. Ice, water and wind transport the eroded material to the lowlands where it is deposited in a coastal basin or on the ocean floor. Here, layer upon layer of mud (shale), sand (sandstone), gravel, boulders (conglomorate) and the remains of plants and animals (fossils) were depositied. Faulting, folding and other earth movements uplifted these low sediments to bring the rocks to where they are now. As Whipstick Gully was frequently mined and quarried in recent times, you get a great view of the millions and millions of years of evolution.
The Three Types of Rock
Igneous Rocks - These form when magma, or melted rock from inside the Earth, cools and hardens. They can form above ground when magma erupts from a volcano as lava. They can also form deep inside the Earth's crust and then be exposed at the surface by the overlying rocks wearing away. The crystals found in igneous rocks have angular shapes. They have not been worn like sedimentary rocks or squished like metamorphic rocks.
Sedimentary Rocks - These form where sediments are deposited long enough to become compacted and cemented into hard beds or strata. They are the most common rocks exposed on the Earth's surface but are only a minor constituent of the entire crust. Their defining characteristic is that they are formed in layers.
Metamorphic Rocks - These were once igneous or sedimentary rocks, but have been changed (metamorphosed) as a result of intense heat and/or pressure within the Earth's crust. They are crystalline and often have a “squashed” (foliated or banded) texture.
Sources:
- 'The structure and general geology of the Warrandyte goldfield and adjacent country' by JT Jutson
- 'If rocks could talk' by The American Museum of Natural History
- 'Amazing Facts About Australian Landforms' by Allan Fox
- Encyclopaeedia Brittanica
- The Geological Society
To successfully log this cache please use your own judgment and the information provided above to answer the following questions and send us your answers to the best of your ability;
1. Based on your observations at GZ and your reading above, is this rock mainly comprised of Igneous, Sedimentary or Metamorphic Rock and why?
2. About 3/4 up the wall there are some horizontal layers that stand out. Are these lighter or darker than the rest of the wall? Can you suggest why this might be?
3. Provide a photo of your team, team name or GPS near GZ. Include this photo in your log, but make sure it doesn't show any of the answers.
You are welcome to log straight away to keep your TB's and Stats in order but please message us with your answers within 10 days. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted.