Newer Volcanics
Your standing atop an area of regional significance as an 'Excellent example of lateral stream development and erosion along rock unit boundaries'.
The W James Whyte Island Reserve, also known as “The Island”, is an isolated volcanic hill that was donated to Conservation Volunteers Australia (CVA) in 2006 by W. James Whyte.
The Reserve is located adjacent to the Werribee Gorge State Park and embraces sections of the Werribee River and Myrniong Creek, and includes important geomorphological sites and areas of remnant vegetation. The Werribee Gorge has been identified as having some of the world's earliest known glacial deposits, and the Werribee River has cut through sediments that were deposited over 400 million years ago.
Who woulda thunk it?!
The Lesson
Mount Blackwood is a prominent scoria dome that is built on lava flows. Scoria is a dark volcanic rock typically pebbled with small holes which indicate gas bubbles that have frozen into place. It is predicted that roughly three million years ago Mt Blackwood's lava flow filled the stream bed of the nearby Myrniong creek. Later, that stream cut a new course beside the basalt. Basalt is a dark coloured rock, usually black, that is commonly formed from lava flow. The lava that flowed over the Island's Permian glacial sediment is now exposed as basalt and is resting on top of the local underlying Ingliston granite, which is exposed as a lighter colour. The lesson here is to identify what evidence lays nearby of the lava flow that is said to have occurred some 3 million years ago, and identifying the exposed Ingliston granite.
Q&A
There is an information sign at GZ which outlines the geology of the area, accompanied by a great diagram. This will help you with your answers however is not essential.
1. Looking to the left of the track on the descent (south), what kind of rock is evident, and why?
2. To the right of the track, north and down the hill, you will see some distinct patterns in the rock. What kind of rock is this? What colours do you see?
Proceed a little up to stage 2.
3. What other kind of rock is present here? How could it have gotten here?
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.
I hope you enjoyed visiting this area, and myself thank Mudbrick for first taking me here.
References: Tempest, G, 2012, Melbournes Western Gorges.