This Earthcache was made possible by Peter Kennett and the Sheffield Area Geology Trust who kindly allowed me to reproduce material from their website. The address is www.geologyatsheffield.co.uk/sagt. You will be able to log a find on this cache by answering some questions on the stone used to build Sheffield's Town Hall.
Sheffield Town Hall
Many of Sheffield's buildings are constructed from rocks which crop out within the region. These include the Millstone Grit Group. All the principal stone beds of this group have been extensively quarried.
Stoke Hall Quarry at Grindleford, in the Kinderscout Grit
Photo by Peter Kennett
The Kinderscout Grit is the oldest of the major Millstone Grit stone beds and forms the extensive and often inaccessible area of the Kinder Scout - Bleaklow moors. It tends to be a very hard stone, which makes it less useful as a building stone. One of the quarries working Kinderscout Grit is at Stoke Hall, near Grindleford, where the stone is a more uniform, medium-grained stone which can be shaped in any direction, i.e. it is a 'freestone'. This quarry supplied the stone used to construct Sheffield's Town Hall, which was officially opened by Queen Victoria in 1897. An extension built with the same material was opened by the Prince of Wales in 1923. The sculptures and balustrades in the adjoining Peace Gardens were installed in the 1990s using matching stone from the same quarry, which is still operating.
Surface Discolouration
Over time, stones used for building can become discoloured. The three main reasons for this are biological soiling, particle soiling and staining. Stone can become biologically stained when organisms such as algae, lichen and bacteria begin to grow on, and in the stone. Particle soiling occurs when pollution, fumes etc accumulate on the stone, discolouring the surface. Finally, staining occurs when darker minerals present in the rock gradually reach the surface.
Specialist cleaning methods, such as sandblasting, can be used to clean building stones. However some cleaning methods do more harm than good, by disfiguring the underlying stone. Some cleaning methods can make the problem worse and increasing future discolouration by making the stone more susceptible to rain, pollution and dirt.
Logging your Find
In order to log your find, please send a message to my profile answering the following questions. There is no information about the stone around the Town Hall, so you may need to do some research to answer these questions, the answers to which are freely available on the internet.
- Go to Waypoint 1 (N53 22.806 W001 28.155) or Waypoint 2 (N53 22.785 W001 28.154). The stone is the same in both locations.
- Describe how the stone looks and feels.
- What type of rock (Igneous, Sedimetary or Metamorphic) is used in the Town Hall and Peace Gardens, and why do you think this?
- What is the name of the stone used (e.g. granite, sandstone, slate, limestone...)? Again, give me your reason for thinking this.
- Which geological period was the stone formed in (e.g. Jurassic, Triassic, Cretaceous, Carboniferous...)?
- Go to Waypoint 3 (N53 22.832 W001 28.160). Stand by the postboxes and face west towards the pillar.
- There are two types of surface discolouration here. What do you think they are? What is your reason for thinking this?
- Given the name of the grit, what industrial use do you think the stone had?
In addition, optionally upload a picture of yourself or your GPS in front of any of the stone around the Town Hall or Peace Gardens. I will respond to your message as soon as I can.