Introduction
Rock hard... solid as a rock... etched in stone... heart of stone - all common expressions which reflect our default perception of rocks which is that rocks are hard, because we are used to seeing them most at the Earth's surface where the temperature and pressure are in the range where rocks are solid.
The fact is though that the rocks we see at the Earth's surface weren't always hard - or even solid, regardless of whether those rocks are sedimentary, igneous or metamorphic in nature. Some rocks, even though they are fully formed, are still soft because they are made up of very fine layers a few millimetres thick.
Geologists can tell quite a lot about the history of a rock, about the forces is has been subjected to and the changes it has undergone, and in what order those changes happened by looking at certain characteristic features.
This EarthCache takes you to the site of a former quarry with exposures of interbedded layers of sandstones and siltstones known as Upper Haslingden Flags. The layers of sedimentary bedrock we see exposed today were formed in a vast river delta environment, approximately 319 to 320 million years ago in the Carboniferous Period.
Logging Tasks
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Based on your observations at the cache location and the information on the cache page, please tell me:
- Estimate the angle of the beds between horizontal (0°) and vertical (90°).
- How many load casts can you see?
- Are the load casts all side-by-side in a single horizontal band or scattered in different bands up and down the quarry face?
- What form or forms of brittle deformation do you see here?
- The load casts represent ductile deformation. Describe any obvious visible relationship between these and any brittle deformation features.
- 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.
Background
Clastic sedimentary rocks (also known as detrital sedimentary rocks) are formed from eroded fragments of older rocks. These eroded fragments, known as sediments, are typically transported by some flowing medium - water, wind or ice, before being deposited.
Because the sediments are laid down under the force of gravity they tend to settle in horizontal layers called beds. Beds are made up of sediments of roughly the same size and type. Sandstone is made up of sand-sized sediments and siltstone is made up of silt-sized sediments.
If the size and/or type of sediments being deposited changes distinctly a new bed is formed. The interface between two beds is called a bedding plane. Beds less than one centimetre thick are known as laminations or laminae.
As the layers of sediment accumulate, the increasing downward pressure on the lower layers causes them to become compacted, forcing out water and leaving behind minerals which act as cement, binding the loose sediments together to form new, solid, sedimentary rock. Together these processes, which transform loose sediments into solid rock are called lithification.
Those are the processes which produced the rock which you see at the cache location - Upper Haslingden Flags. Notice that the exposed face is made up of a number of beds, some of which look very similar to each other and some which look quite different. The thick beds with smoother faces are a hard sandstone. There's also a wide band made up of many thin beds (laminae) which are softer siltstone, also known as shale. Also some of the beds have been subjected to one or more types of deformation - both before and after lithification.
Size Matters - As Does Density
The individual grains of sediment in the shale (siltstone) are tiny. Even very coarse silt grains are around just 0.03mm in diameter. The current that deposited these sediments must have been barely moving and they would have settled very gently to form a low density layer made up of many laminations, with a significant number of empty spaces beween the grains. Geologists call these pore spaces. As the sediments were submerged the pore spaces were filled with water - so we say that the sediments were saturated.
Subject granular, loosely compacted, water saturated sediments to powerful vibration or sudden loading from above i.e. by dumping a large quantity of new sediments on top of the saturated layer and the result is liquefaction.
The impact of the load of more dense sediments landing on the saturated, less dense layer causes the water pressure in the pore spaces to increase to the point where the individual sediments lose contact with each other and the whole body of sediments starts to act more like a liquid than a solid.
In this state, while the sediments are at their softest, lobes of the denser upper layer sink down into the less dense layers below, effectively resulting in deformation of both.
Unsurprisingly, any deformation structures left behind in the soft sedimentary layers while they are in this liquified state are called Soft Sediment Deformation Structures or SSDS for short. Load casts are one common example of SSDS.
What Do Load Casts Look Like?
The short answer is that they vary significantly both in terms of scale / size and in overall appearance.
Remember that load casts are formed by natural forces in soft sediments, so it's unlikely that any two will ever look completely alike - but there are common features and similarities which can help to identify them.
The image at the top of this cache page shows some load casts which are similar to the ones you'll find at the cache location - and here's another image which shows a closer view of a single cast and some of the identifying features:
The most obvious feature is the shape - it's curved, a bit like a wide letter U, or a letter C that's fallen on its back 
The shape results from the thicker, more dense layers (indicated by the black arrow) sinking down into the thinner, less dense layers (indicated by the white arrow) while the sediments were still soft. Soft sediments tend to deform by bending.
Obviously since then the processes of lithification have completed, turning these sediments into the solid rock we see today.
Bend or Break?
One of the forces which shapes rocks is stress. Generally speaking, rocks respond to stress in one of two ways: they either bend or they break, depending on how soft or hard they were when subjected to that stress. When rock bends or flows, like clay, it's called ductile deformation. When rock breaks, it's called brittle deformation. Any material that fractures and breaks into pieces exhibits brittle behavior.
Soft rocks and sediments subjected to stress tend to bend and fold, to flow, resulting in softer, more curvaceous features being left behind.
Hard rocks tend to resist stress more - but only until the amount of stress has built up to the point where it overcomes the integral strength of the rock and the rock cracks, breaks or even shatters, typically resulting in sharper, more angular features. The rapid release of built-up energy that occurs when solid rocks finally succumb to accumulated stress can result in earthquakes.
Rocks which have changed shape in response to stress - whether that be bending or breaking or a combination of the two - are said to have been subjected to deformation.
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Brittle Deformation - visible effects of stress on solid rocks include joints and faults.
If the rock cracks but the rock on either side doesn't move relative to the other side the crack is known as a joint.
If, after the rock cracks, the rock on either side of the crack moves relative to the opposite side, that's known as a fault.
The image to the right shows a very clear fault where the rock either side of the crack has slid up/down, leaving the horizontal layers misaligned.
If you look carefully though, to the right of that fault is a faint crack cutting through the rock, roughly parallel to the fault, and ending in the bottom-right corner of the image. That crack - where the horizontal layers are still aligned - is a joint.
It's not unusual to see a mixture of joints and faults in a solid rock that's been subjected to stress.
If you've carefully read and digested the information from this cache page your tasks at the cache location should prove relatively straight forward, although you may wish to take a printed copy of the page with you so that you can check your answers while there 
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Please submit your logging task responses before posting your log.