The Rocky Beauty Show EarthCache

This cache was nominated in the 2018 Victorian Cache of the Year Awards (Best Location).

This is a park-and-walk cache. Parking is in Faull Close, which is about 200m from the GZ. Please do not try to cross Maroondah Highway. Please stay on the northern, Faull Close side.

At the GZ, if you look across Maroondah Highway, you will see part of the Dargile formation which underlies this part of Melbourne. There are similar exposures of it along the rail line to Melbourne and on the Eastern freeway.

The rocks you are looking are sedimentary rocks and were formed in the Silurian period, about 420 to 440 million years ago. Sedimentary rocks make up to 66% of the earth’s crust, with the remaining 34% being igneous and metamorphic rocks.

Sedimentary rocks are formed by the accumulation of small particles or sediments. There are three basic types of these rocks: those formed from the weathering debris of older rocks; those formed by dissolved chemicals coming out of solution, as in limestone; and those formed from plant or animal debris such as coal and some other limestones.

The rocks you can see are in thin layers, called strata or beds. When formed at the bottom of an ancient sea, they would have been horizontal, and over time were compressed into rocks, and then forced into the angle you see now by movements in the earth’s tectonic plates.

There are two different types visible - sandstone and shale. Both were formed from weathered, older rock particles called clasts. As the name suggests sandstone is formed from sand-sized clasts (particles) - 0.06 to 2mm in diameter. Sandstone can be quite hard and has often been used for constructing buildings, like the Old Treasury Building on Spring Street.

Shale is formed from much smaller, very fine clasts, invisible to the human eye, typically less than 1/256 millimetre in diameter. It is made up of many thin layers, is often quite fragile, and easily breaks into thin flat pieces. It has few commercial uses. The different colours of shale are shown below.

Please answer the following questions to complete this cache and message the answers to the CO. You can log the cache immediately.

1. What are the 3 major types of rock in the earth's crust?
2. What type are the rocks you can see, and what were they formed from?
3. Which of these 2 rocks do you think would be the smoothest to touch?
4. Which of the strata you can see do you think is the oldest, and why ?
5. What do these rocks tell you about the ancient history of this part of the country?

Thank you for visiting; I hope you enjoyed your visit. There is another earthcache you may enjoy about a different aspect of these strata at GC7TBB6 “The Ancient Art of Silurian Rock Folding”.

Thanks to Kezababe and friend for pointing out an error in the narrative.

References:

1. Sites of Geological and Geomorphological Significance on Public Land. VEAC Metropolitan Melbourne Study 2008/9. Final Report May 2009
2. Introduction to Types & Classification of Rocks /li>
3. Sandstone
4. Mudstone & Shale
5. Geology of Melbourne
6. Sedimentary rocks

   There is a video about the formation of sedimentary rocks here

   I am a proud