Please read the whole of the cache listing and answer the questions below.
I read every single email and always respond so please send a message, or email, with answers to the questions below, to log your find.
You may log your find at the same time since the answers are pretty easy.
There is parking close by and the paths are not even or level around the location, however this location is just off the path and all but the most infirm should be able to get there.
For this cache I’d like you to turn your attention to the rocks in this little valley and the thicknesses of the layers of rock.
You will be asked questions about the different thicknesses of rock beds and why they are so.
Sedimentary rocks, how why and where.
Sedimentary rocks are formed from the broken remains of other rocks that are moved to another location, usually by water and become joined together to form new deposits.
A river carries, washes or transports, pieces of broken rock as it flows along. The faster the river the more the small pieces it can carry. When the river reaches a lake or the sea the flow of water slows, its load of transported rocks settles to the bottom. We say that the rocks are deposited as the small particles settle to the bottom. The deposited rocks build up in layers, called sediments. This process is called sedimentation.
The weight of the sediments on top squashes the sediments at the bottom. This is called compaction. The pressure of weight from above means the water is squeezed out from between the pieces of rock and crystals of different salts form. The crystals stick the pieces of rock together. This process is called cementation.
Cementation occurs as the minerals and crystals from each layer form a layer. If the layer of sedimental material is constant it is less likely a distinct layer of different sediment will form. The more often the change in make-up of the minerals deposited changes, the more likely some the cementation is to be of a different structure to the other layers forming many thin week layers.
These processes eventually make a type of rock called sedimentary rock. It may take millions of years for sedimentary rocks to form. The thickness of the resulting rock sediments can vary from a few millimetres to several meters of each layer.
Different thicknesses of rock deposits are possible The thickness of each layer of rock depends upon the flow of water and the way in which it has been deposited. If the same type of material is washed down with steady water flow the depth of the sedimentary rock can be quite constant creating smooth rock with strong bonds. This type of rock is suitable for building because both the bedding planes and vertical strengths are good.
If the water flow is variable into the sea or lake, different amounts and types of material can be washed down creating thin layers of sediment with weak layers of rock. Thin layers of rock generally have weak vertical strength too meaning that it is unlikely that this rock would be suitable for building.
Here you will find both thick and thin layers next to each other. There is no doubt that these deposits must have been made under different conditions and yet in this little gully the thicknesses of deposits are together, you will need to give an explanation for that.
At this location I wish you to inspect the rock and its depths of layers in the narrow gully and around the rock face, this can only be done from within the gully. There are several exposed sections of rock and the information you need, can be gathered at any of these sights.
So hopefully you will have enough information to answer the questions below.
- Please describe the bedding of this rock
- Why are there different thicknesses of bedding? Please explain your answer
- How do you think it is possible that rocks with different properties can be located together?
- Please look down the steep valley you are sighted in and tell me what geological feature is the most obvious
Thank you for visiting the area and attempting this cache.
Please remember to send me your answers via email or message when you log your find.
Please do not include photos that will give away answers to Q4
Happy caching
treboR