Ockleston Memorial water fountain and drinking trough (now planted with flowers) was constructed in 1889 in memory of a popular Cheadle GP, Dr Robert Ockleston, and positioned at the centre of Cheadle Green at the junction of Cheadle High Street and Manchester Road. It was moved from the junction in the late 1960’s to make way for road improvements, but a major renovation in 2017 has seen it relocated close to its original position on Cheadle Green, where it now again forms a prominent feature. Within a few metres of the Ockleston Memorial lies the Cheadle War Memorial; another element to this EarthCache. (Figure 3). An information board is adjacent to the Ockleston Memorial for a more historical perspective on the monument.
(This EarthCache is now part of the Cheadle GeoTrail Audio guide. This provides audio commentary on the geology of 4 EarthCache locations in the Cheadle area: 'Millstone Grind' (GC7MEBC), 'Rock of Ages' (GC7DHPN), 'Death in Paradise' (GC7MM93) and 'Memorial Rocks' (GC7NAFQ). This trail can be accessed by downloading the "SITUATE" app to a smart phone from the App Store and searching for 'Cheadle GeoTrail'. (https://situate.io/). This was produced to celebrate GEOweek 2023).
The Geological Background
The Ockleston Memorial was designed by the architect Alfred Darbyshire (a nephew of George Bradshaw who compiled the famous railways guides) and is made of a combination of Mansfield limestone, Aberdeen granite and metal.
The Mansfield limestone forms the elaborately carved base to the column and fountain. (Figure 1). As it lacks fossils or other structures it is of little geological interest to the non-specialist, although useful as a building stone. This limestone, called DOLOMITE, is composed of calcium and magnesium carbonates that does not rapidly dissolve or effervesce (fizz) in dilute acid as does most calcareous limestone. The carbonates were deposited in a shallow sea that covered north-east England during the Permian period (about 290 - 250 million years ago).
Figure 1
The granite comes from quarries near Aberdeen and its salmon-red colour makes it favoured for use as a decorative stone. Granite forms from the cooling of large bodies of magma typically at depths around 30 km in the crust. Slow cooling allows time for the growth of large (>3mm) interlocking crystals as minerals crystallised out of the magma according to their melting temperatures. Earlier formed crystals often show good crystal shapes whilst later minerals crystallise in between the spaces left and are therefore more irregular.
Granites are made of silicate minerals, typically containing 55-75% silica. The interlocking crystals provide cohesion which adds strength and makes them suitable for polishing without plucking of the crystals and this, along with the high proportion of hard and stable minerals, make granite particularly strong and durable.
Figure 2 shows that granite is made up of essentially 3 minerals, quartz, feldspar and mica.
Figure 2
Quartz is the second most abundant mineral in the Earth’s continental crust after feldspar. The mineral here is typically colourless and transparent with no natural planes of weakness (cleavage planes). The feldspar is divided into two types; white (plagioclase) feldspar and salmon pink (orthoclase) feldspar which gives this rock its distinctive colour and makes it so favoured as a decorative stone. Both feldspars show cleavage planes. Randomly speckled throughout the granite is mica which is typically of the black variety (biotite) which appears shiny in some orientations.
If you look carefully, on the section on the fountain, a quarter of the way around the rim in an anticlockwise direction from the only surviving gabled stone canopy that housed a water fountain, you will find a dark, crystalline “blob” in the granite which seems out of place and looks like a flaw. (Figure 2). This is an ‘inclusion' and is either a fragment of rock which was broken off from the wall of the magma chamber when the magma was forced into the Earth’s crust (a xenolith) or a blob of a different type of magma (an enclave) that did not mix when both were originally molten. Either way it provides an interesting piece of evidence of igneous processes operating some 30km below Aberdeen, 470 million years ago!
With this information, go and compare the Aberdeen granite with the granite making up the War Memorial (25 metres to the North). (Figure 3).
Figure 3
To log this EarthCache please answer the following questions and send by e-mail or through the Message Centre;
1. State the year Robert Ockleston died. (as inscribed in the stone on the top of the column)
2. State the number of sides to the Ockleston Memorial water fountain.
3. State the longest dimension of the ‘inclusion’ illustrated in Figure 2. (Either using a ruler or a coin as a measure - e.g inclusion = 5 x 10 pence coins)
4. State any differences between the granite of the Ockleston Memorial and the granite of the War Memorial. (You can be as detailed or general as your understanding allows).
Please feel free to add photos to the gallery.