At GZ the dark grey rock is limestone and it is fairly localised, being in a belt running 20 km along the valley and 1 km in width. Back in the Devonian period (about 400 million years ago) this whole area was below the surface of a shallow, warm sea. Gradually corals and lime from the seawater were crushed into layers to form the limestone. These layers were then tilted and folded by volcanic movement that has resulted in the rock sticking out from the surface in lines along the valley.
As the sea level finally fell the rock was exposed to the action of rainwater. This rainwater has absorbed carbon dioxide from the air and is therefore mildly acidic. As the limestone is mainly calcium carbonate, it is gradually eaten away by rainwater. The limestone here is very hard and fine-grained and as it is very open to the weather, the rain cuts grooves down the surface of the rock. The resulting fluting (known as rillenkarren) is quite sharp. In the limestone rocks around Careys Cave you will see abundant examples of this weathered fluting known as rillenkarren. Rain water falls on the upper edge of a rock and it then dribbles down the side. As more rain falls upon the rock, the drops continue to run down the rock using the same path. Each drop of rain dissolves a little more of the rock. Over a long period of time the drops dissolve a series of grooves down the rock.
Underground there are many cracks through the limestone and some of these widen into tunnels and then become caves. There used to be a lot or rock (and caves) above surface which have gradually disappeared due to the action of the rainwater. There will be caves under most of the valley floor, however access is very limited due to the red clay sediments covering most of the surface. While many caves you visit are formed by a strong river pattern, Carey's Cave is somewhat different. It is called a phreatic cave which means it was formed principally below the water table. As many tunnels joined and expanded it has resulted in a cave with a very sculptured rock surface. The dropping of the water table has then led to the growth of many crystal formations, but these have also been coloured by oxides from subsequent floodings in years gone by.
Logging Requirements
To claim this Earthcache you will have to head to GZ and collect the answers to the questions below and email these to me for verification using the contact details in this listing. You can log your find once the answers have been sent. I will reply asap and may get back to you for further clarification. Do not log a find without sending me answers as I do check and will delete your found log if I have not received your answers.
Examine the rocks at and near gz and email me the answers to the following questions (note there is no need to cross the fence to answer any of the questions):
- Describe the rocks next to the picnic shelter:
Rock colour/s?
Are all the rocks fluted? Why has this happened?
Do the rocks display any other features? How do you think these features have formed?
- Look east and west of gz. How does the landscape differ?
What do you think has happened to create the difference in the landscape?
I love to see photos of cachers exploring this area. If possibile include a photo in your log of your group near gz. Please do not give away answers to the cache questions with your photo.
Getting There and Cave Information
The village of Wee Jasper is located in the Goodradigbee Valley approximately 35 kilometres north-west of Canberra and 54km south-west of Yass. The Yass - Wee Jasper Road provides a scenic route or from Canberra, the Wee Jasper Road is accessed via Uriarra Road, a slightly circuitous 86km drive.
Guided tours of Careys Cave are conducted regularly on weekends - the gate may be closed at times but you can still walk into gz (see website for details
www.weejaspercaves.com). The cave tours are suitable for all ages with easy access on well-lit pathways with a minimum of steps. There are camp grounds in the area, as well as a range of farm stays and a hotel with restaurant and cabins (note no petrol is available in the village of Wee-Jasper).