The co-ordinates put you in the centre of Rev. Urijah R. Thomas’ Memorial Fountain. This large structure, incorporating a fountain, clock and weathervane, was designed and erected by J. Whitehead and Sons of London and Aberdeen in 1904. Despite walking past this for many years, I never noticed this memorial in full until recently. From afar, it may appear nothing more than an archaic monument lost to time. However, when appreciated up close we see a fusion of different materials and minerals which form a very elaborate and complex piece of architecture; well worth a closer examination via a trusty and involved earthcache!

The pavilion enclosing the fountain is octagonal and stands on a granite platform of five steps. On this are eight additional granite columns, with moulded bases and Doric capitals, each carved from a single stone. These and the huge central column of red sandstone, support the octagonal entablature and roof of pitch pine and Broseley tiles. Around the central column are four circular granite drinking basins. All the visible woodwork on the roof and the surmounting clock turret is oak. The turret roof is covered with copper and surmounted by a vane.

Please do not attempt this earthcache expecting it to be a quick “drive by” cache, see the attributes. The D3.5 rating here is also intentionally higher than usual for an urban earthcache; we have included several distinct (yet connected) geological topics, thus there are more questions than usual. Some of these questions require careful consideration of the information presented below and subsequently detailed answers. The amount of explanation expected varies by question; some require only a few sentences, while others require more to ensure all parts of the question have been thoroughly answered. Good luck and enjoy it! 🎉

Granite
 

Granite is an intrusive igneous rock, meaning it is formed from cooled magma beneath the earth's surface. It occupies 70-80% of the earth’s crust. The main two crystals you’ll find in granite are feldspar and quartz, which together make up over 80% of its volume. The composition of these minerals, along with many others, are what gives granite its colour. Below is a list outlining the primary colour of these minerals, which help us identify what the overall colour of granite is likely to be. Note that many of these minerals can be found within some or even all granite colours. The overriding colour comes down to the combination and ratio of each mineral that is present within the rock.

• Quartz: Milky White or Colourless
• Feldspar: Off-White
• Potassium Feldspar: Light Pink to Red
• Biotite: Black or Dark Brown
• Muscovite: Light Gold or Light Yellow
• Blue Labradorite: Blue
• Amphibole: Black or Dark Green

Given its durability, granite can resist abrasion and bear significant weight. It is also considerably inert and can be polished to achieve a brilliant finish. Polished granite also serves as a viable protective layer, forming a barrier between the stone’s pores and external weather – reinforcing the granite’s ability to resist severe climatic conditions. Granite is mined worldwide but Aberdeen in Scotland is often referred to as the ‘Granite City’ due to the extensive production of the titular rock.

Xenoliths
 

Simply, a xenolith is a piece of rock trapped in another type of rock. Most of the time, a xenolith is a rock embedded in magma while the magma is cooling. As magma rises through pipes (i.e., cracks) between the earth's crust and mantle, pieces of the surrounding rock can be torn off and become trapped in the magma.

The rock that forms from cooled magma is called igneous rock. Xenoliths are usually visible, see above image, often having a different colour and density than the surrounding rock. Xenoliths vary in size, being as small as a grain to as large as several meters in length. There are a number of examples of xenoliths within the granite of this memorial. Xenoliths can be a piece of rock trapped in a piece of sedimentary rock, but this is rare.
 

Sandstone
 

Sandstone is a type of limestone, a sedimentary rock with a high sand content and compacted by a cement-like calcium carbonate or iron oxide. Its formation occurs over thousands/millions of years when grains of sand are compacted and cemented together. The sand grains often are composed of the minerals quartz or feldspar that were worn off other rocks and ground down into pebbles. Sandstones vary in their composition to produce the different tonalities, often exhibited by the material once it has been worked into the various formats used in buildings.

Sandstone is composed mostly of quartz grains, which are made of silica that does not break down chemically, but it can also contain significant amounts of feldspar, and sometimes silt and clay. Sandstones are resistant to chemical weathering when held together with a quartz cement, but wherever the cement is either clay or iron rich or missing, the sand grains become loose and will be washed out much more easily.

Logging requirements
 

To log this cache as found, please answer all questions below and use the geocaching message, or email, system above to send us these answers. Use information from the cache page above and your observations at GZ to do this. You can log a find once we have been sent a message; there is no need to wait for a reply. We may delete your log if your answers are hugely incorrect or show no attempt to engage with the geological lessons presented above. Please also do not post any answers in your log or photo; doing so risks spoiling the cache for other cachers and will result in your log being deleted without warning. Note the below image is needed for some of the later questions.

1. Study the two different types of granite used for the eight columns and platform/steps. For both types, what are the three main minerals present? How does this explain the differences in colour? Provide estimates of the different ratios and relative sizes of the minerals.
    
2. Describe the physical differences (i.e., how they feel) between these two types of granite, identifying which is polished granite and which is not. Why do you think only one of the types of granite used in this monument is polished?
    
3. Majority of sources describing this memorial detail that the stone used for the columns, plinth and drinking fountains is red granite. Do you agree with this? If not, which colour granite do you think this actually is and which sole mineral largely determines this?
    
4. Now focus on the eight granite columns. Locate the largest xenolith you can find. Referring to the numbering system in the above image, which column is this xenolith in? Describe its colour and where it is located on the column.
    
5. Locate another xenolith on a different column. Which column is this and where exactly on the column is the xenolith located? Describe the differences, if any, between this and the previous xenolith you studied. Does your observation suspport the statement that the granite used for all eight stone columns was mined in the same place? Explain your answer.
    
6. Can you find any xenoliths in the granite platform/steps? If so, where are they in relation to the numbered granite columns? Are they smaller or larger than the xenolith you identified in question 5? Why might they be different in size and colour compared to the xenoliths in the granite columns?
    
7. Finally, study the red sandstone which makes up the central column of the monument. Describe the rock in terms of its texture, hardness, surface appearance and grain size/feel.
    
8. Would you agree that the sandstone used for this monument’s central column mainly consists of quartz cement? If no, what do you think this sandstone could consist of instead? What does this indicate about the use of this sandstone for the central column rather than the exterior, more exposed, columns? Explain your answers carefully.
    
9. To prove that you visited the GZ on the date you did, feel free to include a picture of yourself (face not necessary) holding a piece of paper with your caching name and date clearly written on it and with the whole memorial in the background. Please ensure that you do not spoil the answer to any of the questions in your photo. 📷