Introduction
The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 Mya (Million years ago), to the beginning of the Permian Period, 298.9 Mya.
This EarthCache is in the midst of an area that, during the early Carboniferous, was subjected to crustal extension (stretching). Much later, in the late Carboniferous, this same area was subjected to crustal compression (squeezing). This stretching and squeezing subjected these rocks to enormous amounts of stress in the form of tension and then compression and those stresses changed the shape of the rock layers, tilting layers which were previously roughly horizontal and even creating curvaceous folds which remain to be seen today.
This area previously being dominated by a shallow carbonate sea has resulted in a mixture of rock layers including limestone, sandstone, shale and mudstone.
Rather helpfully for us, flowing water has subsequently cut down through the solid rock over a long period of time so that we can see the layers which formed millions of years ago, and decide if we are looking at an anticline or a syncline at this particular location.
Logging Tasks
IN ORDER TO COMPLETE THESE LOGGING TASKS PLEASE EMAIL YOUR ANSWERS TO US VIA OUR GEOCACHING PROFILE BEFORE SUBMITTING YOUR LOG. PLEASE DO NOT INCLUDE ANSWERS IN YOUR ONLINE LOG. YOU CAN GO AHEAD AND LOG YOUR FIND AS SOON AS YOU HAVE SENT YOUR ANSWERS IN ACCORDANCE WITH GROUNDSPEAK GUIDELINES. LOGS WITHOUT ADEQUATE LOGGING TASK EVIDENCE MAY SUBSEQUENTLY BE DELETED.
- Looking at the folded layers of rock here, and remembering that they were laid down approximately horizontally, which stress do you think reshaped the rock as you see it today? Was it tension, compression or shearing stress?
- Considering the curvature of the rock, would you say the fold is an example of brittle behaviour, ductile behaviour or a mixture of the two? What observations did you make to arrive at your conclusion?
- Looking at the concentric layers of rock and taking into account your responses to all of the previous logging tasks, do you think this rock was always at the surface, as it is now, or do you think it might have been deeper / had more rock on top of it? How did you come to this conclusion?
- Has the stream cut through the curve parallel to the axial plane or perpendicular to it?
- Is this fold an anticline or a syncline?
- Optional task: feel free to add any photographs of your visit that do not show the specific features from the logging tasks - no spoilers please. In the interests of allowing everyone to experience the EarthCache fully for themselves obvious spoiler photographs will be deleted.
Steno's Principle of Original Horizontality
As recently as (in geological terms) 1669 a Danish scientist by the name of Niels Stensen, better known by his Latinised name of Nicolas Steno put forward three defining principles of the science of stratigraphy - the branch of geology which studies rock layers (strata) and layering (stratification), primarily used in the study of sedimentary and layered volcanic rocks. These laws or principles, known as Steno's Laws or Principles are still in use today 
. . . strata either perpendicular to the horizon or inclined to it, were at one time parallel to the horizon.
Steno reasoned strongly tilted rocks did not start that way - that all rock layers (strata) started off essentially horizontal, but were affected by later events—either upheaval by volcanic disturbances or collapse from beneath by cave-ins. Today we know that some strata start out tilted, but nevertheless this principle enables us to easily detect unnatural degrees of tilt and infer that they have been disturbed since their formation. And we know of many more causes, from tectonics to intrusions, that can tilt and fold rocks.
It stands to reason that because of the way sedimentary rocks are formed, under the force of gravity, that the layers in them would all be flat / horizontal, and many sedimentary rock deposits do indeed look precisely that way - so what would cause them to be otherwise? What would cause them to look like the rocks you will see in the process of completing this EarthCache?
Stresses in the Earth's Crust
The Earth's crust changes shape in response to different types of stress which arise from phenomena such as the movement of individual rock plates that make up the crust. Three types of stress are:
- Tension
- Compression
- Shearing
Before we look at those three different types of stress let's imagine a series of rock layers (strata) which haven't been subjected to any stresses and let's assume that they were laid down horizontally, just as Steno said they should be:
Here we see a stratigraphic section - a sequence of sedimentary layers stacked one atop the other.
The layers here are shown in different colors, suggesting layers of different types of rock but stratigraphic units are often made up of individual layers of just one rock type too. The rock on which this Earthcache is based is made up of limestone and sandstone with some mudstone and shale.
The sediments have been laid down horizontally under the force of gravity and at this point have not been subject to any of the stresses which can be found in the Earth's crust.
Tension
According to the scientific theory of plate tectonics the rock plates which make up the Earth's lithosphere (the crust and upper mantle) move around - although much too slowly to be seen with the naked eye 
.
When two of these plates move away from each other the rock between them is pulled in two directions at the same time, creating tension in the rock. That tension causes the rock between the plates to stretch out and become thinner in the middle. The blue arrows in the diagram represent the divergent forces, pulling the rock simultaneously in two different directions, resulting in the thinning in the middle section.
Compression
Compression arises when tectonic plates move toward each other. The mass of the moving plates is so great that the convergent compressive forces are strong enough to squeeze the rock between them until it either folds or breaks.
Whether the rock folds or breaks under compression is not dictated by the compression alone. The other factors which can impact on this outcome are important to the logging tasks for this Earthcache and will be covered further down the page.
Shearing
Stresses which are offset from one another and push a mass of rock in two opposite directions at the same time are known as shear stresses.
Shearing is a type of stress that differs from tension and compression. Tension pulls the layers in the rock and causes them to become thinner in the middle. Compression squeezes the layers in the rock and causes them to thicken or to fold or to break.
Shearing on the other hand can cause masses of rock to slip past each other as they are pushed or pulled in opposite directions by opposing forces.
Folded Rocks - Anticlines and Synclines
Geologists use specific scientific words to describe upward and downward folds in rock strata, and of particular features within them which will be useful for this EarthCache's logging tasks 
.
The axial plane is an imaginary line which bisects the curved rock unit (or cuts it down the middle, if you prefer). The curved layers of rock either side of the axial plane are called limbs. In simple terms*, a curve where the limbs run down toward the axis is typically known as a syncline and the opposite case - a curve where the limbs run up toward the axis is typically known as an anticline.
An easy way to remember which is which as that Anticlines form an A shape and Synclines form the bottom of an S shape.
*By definition an anticline has the oldest layers of rock at its centre or core and a syncline has the youngest layer of rocks at its centre or core. If a unit of rock is inverted (turned upside-down) before being folded that would result in synclines with limbs which run up toward the axis and anticlines with limbs which run down toward the axis - but the means to work out whether or not the layers of rock at the published coordinates have been inverted since they were laid down is beyond the scope of this Earthcache - so we are going to assume that the layers have not been inverted .
Properties of Materials - Brittle vs Ductile
We tend to think of rock being a pretty hard material, which it is, but at the temperatures and pressures found at the Earth's surface it is also brittle and will tend to break rather than bend when subjected to large amounts of stress. At greater depth though, deep down below the Earth's surface it's a different story. As depth increases, temperature and pressure increase and under greater temperature and pressure rock tends to become more ductile - more able and more likely to bend than break.
Properties of Materials - Elastic vs Plastic
At the temperatures and pressures found at the Earth's surface rock tends to be brittle - but if subjected to sufficient stress rock will still bend - but only so far - and will tend to spring back to its original shape if the stress is released, just like a piece of elastic - which is why this type of deformation of the rock is known as elastic deformation.
Elastic deformation will only allow the rock to bend so far before it breaks. The point at which the stress causes the rock to break is known as the yield point or the elastic limit.
Deeper in the Earth's crust, where temperatures and pressures are higher and the rock becomes more ductile it can bend beyond the elastic limit without breaking. At this degree of bend the deformation is known as plastic deformation. Rock which has been subjected to plastic deformation beyond the elastic limit tends to retain its deformed shape rather than spring back to its original shape - the deformation becomes permanent.
That was a lot of words and terminology so let's summarise that with a simple diagram:
If you've made it this far and can apply everything you've learned to the folded rock at the published coordinates then you're ready to tackle the Logging Tasks - good luck! 
You may wish to take a printed copy of the page with you so that you can check your answers while there .
Please submit your logging task responses before posting your log.