About SideTracked Caches
This cache belongs to the SideTracked series. It is not designed to take you to a magical place with a breath taking view. It's a distraction for the weary traveller, but anyone else can go and find it too. More Information can be found at the SideTracked Website
This cache brings you into the heart of the Potteries, home to the pottery manufacturing industry in Britain. At the entrance to Stoke-on-Trent railway station, a statue pays tribute to Josiah Wedgwood, famed for founding the Wedgwood pottery company, and for industrialising the pottery manufacturing process. It is this statue that is the focus of the EarthCache.
Logging Tasks
Q1 - Describe the appearance of the stone that you see. Make reference to its colour and texture.
Q2 – What type of weathering can you see evidence of on this stone? Is there a side on which it is more prominent? Give examples of how this weathering has impacted the stone that you see.
Q3 - The parts of the rock most impacted by weathering are at the bottom of the large sandstone plinth, why do you think this is?
Q4 – if you wish, take a photo of yourself, or something belonging to you, in front of the statue, without revealing any of the answers. This is an optional task.
Sedimentary rocks – Sandstone
The plinth of this statue is constructed from sandstone, a sedimentary rock. Sedimentary rocks are formed over long periods of time, as layers upon layers of sand, silt and clay (sediments) are deposited on top of each other on the sea bed.
Sandstone is a relatively common sedimentary rock, often containing quartz, but the presence or quantity of different minerals and its originating environment can alter the colour or texture of the sandstone. As a relatively durable, but easy to carve stone, sandstone has long been used in construction and decoration, but this EarthCache will focus upon the vulnerability of the sandstone to weathering.
Weathering
When you see this statue, you will most likely pick up upon the effects of weathering on the statue, but what is weathering, and what is the difference between weathering and erosion?
Weathering is the breaking down, altering, or natural destruction of rocks, at or near the Earth’s surface. The key difference between weathering and erosion is that weathering happens in-situ, whereas erosion involves the movement of material (such as landfalls from cliffs). There are 3 principal types of weathering – physical, chemical and biological. This EarthCache will focus on the physical weathering that takes place in rock from this location.
Physical weathering
Physical weathering breaks rocks into smaller pieces, but without any chemical changes to the rock’s composition. This can include freeze-thaw weathering (water entering through cracks, before freezing and then expanding the cracks), thermal expansion and contraction (repeated heating and cooling that causes minerals to expand and contract at different rates, which weakens the rock), or salt crystallisation (salt crystals grow on the rock, causing staining, from where salty water has entered the rock’s pores and cracks.
Part of the physical weathering that you can see at GZ is known as exfoliation, or onion skin weathering, which is where the outer layers of a rock peel or flake away, due to the repeated expansion and contraction (through changes in water absorption levels) of the rock's surface. Sandstone is a naturally porous rock, so as water is absorbed into the rock, salts get left behind and crystalise, pushing the outermost grains apart and causing thin layers to detach.
Sandstone around Stoke-on-Trent
The geology of the Stoke-on-Trent area records a long history of changing environments spanning hundreds of millions of years. Much of the region is underlain by Carboniferous Coal Measures, deposited approximately 320–300 million years ago when the area lay close to the equator. Vast tropical swamps, river channels, and floodplains accumulated thick sequences of mud, sand, and plant material, which eventually formed the coal seams that fuelled the development of the Potteries and local mining industry.
Around 50 million years later, during the Triassic Period, the landscape changed dramatically. The tropical coal swamps disappeared and were replaced by an arid desert environment crossed by large braided rivers. These rivers deposited extensive layers of sand and pebbles that later became the red sandstones of the Sherwood Sandstone Group, which are exposed at many locations around Stoke-on-Trent and North Staffordshire. The sandstone visible at this EarthCache is part of this geological story, preserving evidence of ancient environments that existed more than 240 million years ago.
During the Ice Ages, glaciers and meltwater further modified the landscape, leaving behind deposits of clay, sand, and gravel that cover much of the underlying bedrock today. However, where sandstone is exposed, it provides an opportunity to observe geological processes acting directly on the rock surface.
Exfoliation Weathering
One of the most striking features visible at this site is exfoliation weathering. Exfoliation is a form of physical weathering in which the outer layers of rock separate and peel away in thin sheets. This process creates curved surfaces and flaking layers that can resemble the layers of an onion.
Exfoliation occurs because the surface of the rock experiences different conditions from the rock beneath. During warm periods, the outer layers expand slightly as they heat up. When temperatures fall, the rock contracts again. Although the amount of movement is extremely small, repeated cycles over many years create stresses within the sandstone. These stresses can cause cracks to develop parallel to the rock surface, eventually allowing thin layers to detach.
Water also plays an important role. Rainwater enters existing cracks and bedding planes, weakening the rock and helping to separate weathered layers from the fresher rock beneath. Once a thin sheet begins to loosen, wind, frost, plant roots, and gravity can accelerate its removal.
Please send your answers to the above questions via email, or the message centre, when logging your find. Any logs that are not accompanied by question answers, I reserve the right to delete. I hope that this cache provides you with a welcome break to your travel, or gives you an interesting insight into the local geology.