Welcome to the My Third Favourite Local Volcano earthcache. The hill you see to the south-west is Green Hill. It's about 150 metres above sea level at its highest point and about 45 metres higher than the surrounding countryside. It's on private land, so no crossing the fence and walking to the top to go exploring.
According to the Victorian Resources Online (VRO) Agriculture Victoria website:
“Green Hill is a breached scoria cone with a remnant shallow crater. Lava flows extend to the north and south while the northern and western slopes are littered with blocks of scoria and broken basalt. Some lava and scoria blocks contain fragments of clays containing casts of marine fossils. These have been derived from Tertiary sediments and carried upward by explosive eruptions as inclusions in lava bombs. It is a major topographic feature of the Werribee Plains and an unusual example of fossil material included in volcanic rocks. It illustrates the nature of part of the sub-basaltic geology that is otherwise completely buried by lavas.”
Wikipedia tells us that although the category 'Tertiary' has been superseded it refers to the geological period from 65 million to 2.58 million years ago, a period that began at the demise of the non-avian dinosaurs.
Whatever category we want to call it, those marine fossils were deposited in the clay a long time ago.
Now it's time to put on your earthcache-goggles. At GZ you will see three special rocks with a connection to the volcano. I'll ask you three questions and you send me a message with the correct answers.
Feel free to log your find immediately. As a bonus I'll add a virtual koala stamp to the online log if your correct answers that you send me have a valid reference to chocolate! Please be mindful that if I haven't received your correct answers after seven days I'll delete your log entry.
Q1 What's the special name we might call that roundish, broken rock that has a centre and separate outer shell? (refer to the description if you need to). Q2. One of the brown coloured basalt rocks here has a cream coloured smear across one side. What is the cream coloured smear made of? Q3 Why is one of the rocks so easy to lift?
Happy Geocaching!