Wood Green Drinking Fountain
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Geology of the fountain
The fountain consists of a grey granite trough on a grey granite base, a carved Portland stone fountain head, a red granite drinking bowl, and a red granite panel.
Granite is an igneous (volcanic) rock primarily composed of coarse quartz, feldspar, and plagioclase crystals. It forms from magma that cools slowly underground.
The different colours present in granite are commonly produced by the following:
- Quartz - typically milky white colour
- Feldspar - typically off-white colour
- Potassium Feldspar - typically salmon pink colour
- Biotite mica - typically black or dark brown colour
- Muscovite mica - typically metallic gold or yellow colour
- Amphibole - typically black or dark green colour
The deeper red colour of the granite used in the fountain may come from iron oxide impurities as well as potassium feldspar.
Portland stone is a type of limestone. It is a very popular building stone that has been used in many public buildings in London. It is valued for architecture because it is relatively resistant to weathering for a sedimentary rock, but can still be readily worked by masons.
Portland Stone formed in a marine environment during the Jurassic period, on the floor of a warm, shallow sea. These conditions promote the precipitation of calcium carbonate in the water in a similar manner to limescale build up in a kettle.
On the seafloor, small particles of sand and shell fragments are rolled around by the waves and gradually coated with accumulating layers of calcite. Over time, billions of these balls became partially cemented together by more calcite to form limestone.
Weathering of the fountain
Weathering is a term that describes the breakdown of rocks. There are many different ways in which weathering occurs, but I will just cover the most relevant ones here.
Mechanical Weathering: Water is often a key agent of mechanical weathering via the freeze-thaw cycle. Water can seep into cracks in the rock. When the temperatures drop low enough, the water will freeze. When water freezes, it expands. The ice then works as a wedge. It slowly widens the cracks and splits the rock. As well as natural cracks in the rock, freeze-thaw can also affect a man-made cavity such as a trough or basin.
Chemical Weathering: Chemical weathering changes the molecular structure of rocks and soil. A common form of chemical weathering is when carbon dioxide from the air or soil combines with water in a process called carbonation. This produces carbonic acid, a relatively weak acid that can dissolve rock, and is especially effective at dissolving limestone.
Air pollution can increase the rate of weathering. Burning fossil fuels such as coal, gas and petrol releases nitrogen oxide and sulphur dioxide into the atmosphere, which combine with rainwater to form sulphuric and nitric acid. This phenomenon is called acid rain and has the potential to be much more strongly acidic than the natural carbonic acid.
Biological weathering: This refers to the effects of plants, fungi and animals. For example, a seed that has sprouted within a cracked rock can slowly widen the crack as it grows, and even break the rock into pieces, like a weed growing through pavement. Even small plants, such as mosses and lichen, can enlarge tiny cracks as they grow, and leach minerals from the rock. Damage caused by humans can be considered biological weathering.
At the time of cache publication, the limestone has been treated relatively recently with a biocide that kills moss, algae and lichen, as part of restoration works.
History of the fountain
The Wood Green Drinking Fountain and Cattle Trough was built by the Metropolitan Drinking Fountain and Cattle Trough Association in 1901.
It is a Grade II listed asset, owned by the Local Authority and is currently on the Historic England Heritage at Risk Register.
The Metropolitan Drinking Fountain and Cattle Trough Association was set up in London in 1859 to provide free drinking water. The fountains were often sited outside pubs, to try and encourage the population to drink water rather than beer. This Drinking Fountain is sited outside what used to be the ‘Fishmongers Arms’, which is now a police training centre.
During the 1960s the pub was a venue for rock music, which hosted early performances by musicians and bands that would go on to become famous, including Cream, Julie Driscoll, Long John Baldry, Rod Stewart, Fleetwood Mac, The Kinks, Led Zeppelin and Pink Floyd.
The drinking fountain is not in active use these days, but it has undergone some recent restoration work due to its status as a historical structure that tells the story of the Victorian philanthropists who provided drinking fountains all over London.
Questions to answer
Important note: due to recent restoration works, not all the stone that appears to be limestone actually is, as some voids have been filled with hydraulic lime mortar. Portland stone can be positively identified by the presence of shells and other fossils (although Portland stone does not always contain fossils).
1. Briefly describe the three types of stone that make up the fountain, in terms of grain/crystal size, texture and colours present. Note any fossils present in the rocks – can you spot any areas that are particularly dense with fossils?
2. Considering their properties, why do you think each stone was chosen to be used in their specific locations in the fountain?
3. In the Portland Stone on the West side of the fountain, there is a very obvious replacement from the recent restoration works. What is it?
4. Compare the granite and the Portland stone. Which is in better condition?
5. What properties of the rocks caused this difference? Consider grain size, rock type and composition. What types of weathering do you think have affected each rock?
6. Walk south to the waypoint at The Parish Church of St Michael. This church was built in 1843, and designed by George Gilbert Scott.
Take a look at the stature of Christ in an alcove on the east side of the church. The statue and alcove are carved from some yellow, grey and red coloured sandstones, another sedimentary rock like limestone, but composed primarily of silicates rather than calcium carbonate.
Considering the ages of the Church and Fountain, compare the condition of the two sedimentary rocks. In what ways are they different and similar in terms of how they have experienced weathering?
7. (Optional) Feel free to include a photo of yourself at the cache site or the church, but please avoid using photos that could spoil the answers for other cachers.