This cache is all about some rocks in an unlikely place.
The co-ordinates take you to some rocks. There are 6 of these rocks nearby.
What are these rocks?
How did they form?
Why are they here?
These rocks are granite boulders
Granite is an igneous coarse-grained crystalline rock. Igneous rocks form when rocks melt to form magma deep within the Earth's crust. As the magma rises through the Earth's crust, it slowly cools and solidifies and granite is formed. Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified. The more slowly the magma cools, the bigger the crystals. If the magma cools slowly, large crystals form in the rock. This can happen if the magma cools deep underground. Granite is an example of this type of rock. Granite is an intrusive igneous rock because it forms from magma underground.
This granite has distinctive large pink crystals. These crystals are a mineral called orthoclase feldspar. The rocks also contain a grey glassy mineral called quartz, a dark mineral called biotite mica and another type of feldspar, a white crystal called plagioclase feldspar.
These rocks formed many many years ago.
The granite is very similar to Shap granite from Cumbria. Shap granite was intruded late in the Caledonian orogeny around 394 million years ago.
Why are these rocks standing here in such stage surroundings?
It is likely that these rocks were transported south as ice sheets flowed south from the fells of Cumbria. One of the rocks has deep parallel grooves. These might be glacial striations. Striations are scratches or parallel grooves that result from the action of moving ice, e.g. a moving ice sheet. They form when a glacier moves and rock fragments and sand grains in the base of the glacier or bed rock act as cutting tools.
Another possibility is that the boulders were moved into strategic positions to be used as way-markers. That doesn't really explain the collection of rocks here. They are often found next to riverbeds where rocks from a river’s source have been washed down or on flood plains, where seasonal flooding leaves rocks behind after the water recedes or where ice flow has pushed a wall of eroded material in front of it before receding to leave the rocks behind. Whatever the reason, it is intriguing to see these rocks remain where the surrounding area has been developed.
To claim this Earthcache please email me the answers to the following questions.
1. Examine one of the boulders, and describe the crystals exposed on the surface? How many different types of crystals can you find?
2. Describe the largest crystals? What mineral might they be?
2. Assuming this granite formed at a similar time to Shap granite, during which geological period did this granite form?
4. What evidence is there that these rocks may have been carried here by an icesheet?
In keeping with Earthcache rules, photographs are now optional and I cannot require these to be posted. A photo speaks a thousand words though, so if you have a nice photo of any combination of you, your GPSr and the stones. I hope you will choose to post one to the cache page anyway!
Please email me the answers to questions 1, 2, 3 and 4 and post your photo in your log. Please do not post the answers to questions 1, 2, 3 and 4 in your log. Logs with this information in will be deleted.