Dropstones are fragments of rock embedded within sedimentary rocks. They can range in size from small pebbles to boulders. Collers Beach features a platform of Wandrawandian siltstone which has a wide range of dropstones of different sizes and compositions. This earthcache will take you to two particularly interesting stones, but please take the time to wander around the platform and find more.
At GZ you are standing on the Wandrawandian siltstone. Please be aware that this whole area is underwater when the tide is high and the rocks are often very slippery until they have had a chance to dry. Once the tide has fallen, access is very easy and the rocks dry out. However, please take care when walking on the rock shelves and keep a close eye on geokiddies.
How did these stones become embedded in the siltstone?
300 million years ago (MYA) Australia was part of the super-continent Gondwana. Around 290MYA sea levels rose and flooded the coast, leading to the deposit of fossiliferous sediments which eventually became around 800m thick and which are known as the Shoalhaven Group. Between 270MYA and 80MYA, Australia was much closer to the South Pole than it is today. Ice-fields covered much of Victoria and, as glaciers calved, icebergs floated Northwards. These icebergs carried rocks varying from tiny pebbles to huge boulders and, as the icebergs melted, the rocks dropped into the sediment and are visible today as embedded drop stones. The stone seen here is just one of many drop stones to be found in this area.
How to log this earthcache
In order to log this earthcache you must answer the following questions. You do not have to wait for a reply before logging your find. I attempt to reply to all e-mails submitting answers and, if there are any problems I will contact you to obtain more information.
Q1. At the posted coordinates you will find a large dropstone embedded in the side of a large step (or very small cliff). One of the vertical faces of this stone is brightly coloured. a) What colour is the face; b) approximately how wide is the coloured part?
Q2. At WP2 is another large dropstone, approximately square. Please describe the colour and texture of this stone.
The answers to these questions should not be included in your log, nor should your log include spoiler photos of these two rocks. Please send the answers to me via e-mail. You may choose to use the new message centre if you wish, but please be aware that I rarely go to the message centre and may not see your answers for some time.
If you wish, please take a photograph of your GPS at a different dropstone and post this in your log. This is not required, but would be appreciated.