Geological Forensics 16 EarthCache

This EarthCache demonstrates how Geology and Forensics are often used to together to explain features we find in rocks.

Part of a series of EarthCaches that demonstrate how Geology and Forensics are often use together to explain features we find in rocks.

This simple EarthCache gives an insight into one of the rock types we see used in our city centres, requiring the cacher to study a World War One memorial located within the open-access large church yard of St. Mary’s Church. The memorial can be driven directly up to it if required, and is accessed via wide pavements and/or manicured grass, so is totally accessible for wheelchairs and strollers. The church grounds have many tarmacked paths crisscrossing it, making this available 24 hours a day, although I recommend doing this EarthCache in daylight. There are limited car-parking spaces 15m away from the memorial around the main entrance to the church, or one could park in the nearby residential streets. Buses frequently pass this church, and stop very close by.

Geology is the study of the Earth; its rocks; its structure; everything within it - and also the processes that shape its surface. Forensics is the use of science and technology to investigate and establish facts. Geologists, and especially palaeontologists, use the evidence found in rocks to deduce the environment that a sedimentary rock or fossil was deposited in, or the 'story' of how the crystals in a metamorphic or igneous rock formed.

As stated, there are three main types of rock:

1 – Igneous Rocks

These form when molten rock (known as ‘magma’), cools. As a general rule, the slower it cools, the larger the crystals found within it, and vice versa.

• Granites generally have larger crystals, cooling slowly underground over millions of years.
• Basalts are formed by magma being extruded as lava at the Earth’s surface from a volcano, cooling quickly, forming small crystals.
• Obsidian is formed in the same way as basalt, but cool very rapidly, forming microscopic crystals, giving a glassy appearance.

2 – Sedimentary Rocks

• These form when older rocks have been weathered and eroded, then transported, and then deposited, usually in layers.
• Individual layers can often show evidence of what happened at the ancient surfaces; footprints, worm trails, ripple marks created by waves lapping the shore, and many other such features (including the presence of fossils), can all help us deduce the actual environment the layers were deposited in.
• Over time, these layers are then squashed by the weight of overlying sediments, slowly turning the sediments into sedimentary rocks.
• Common examples include:

• Mudstone and sandstone - the names are determined by the size of the ‘grain’ in the rocks (mud being a smaller grain size than sand). They could have been deposited on dry land, in rivers, or in the sea.
• Limestone – generally formed in ancient warmer, shallow seas (e.g. like the present day barrier reef off NW Australia), these can be formed around beautiful coral reefs, where fish, snails, worms, and various shells all lived, inter-acting with each other as a community, living in and on the mud and sand that made up the ancient sea-floor.
• Coal – formed in ancient (up to 300 million year old!) swamps, full of massive trees, ferns and other plants.

3 – Metamorphic Rocks

• These form when older rocks are buried deep within the Earth’s crust over millions of years, squashing and heating the rocks, so deforming them and causing the original structure within the rock to crystalise or re-crystalise, depending on the original rock. Common examples include:

• Marble – formed when ancient limestones are crystalised, destroying the delicate fossils that may have been present
• Slate – formed when ancient mudstones are crystalised, squashing the mud grains together, then turning these grains into flatter minerals, all elongated in the same direction, so giving slate its characteristic property of being about to be easily split (e.g. for roof tiles)
• Schist – formed when slate is further deformed, causing the already-elongated minerals to grow larger and more prominent
• Gneiss (pronounced ‘nice’) – formed when schist is further deformed, causing the already-elongated minerals to grow even larger still, giving the rock a ‘banded’ appearance.

At the coordinates, one will see a World War One memorial with a wider base, upon which sits a large tall cross. 

As usual with EarthCaches there is no physical cache. To Log this EarthCache, please study the World War One memorial, then email me the answer to these questions:

On the northern side of the memorial is an inscription. Below this is the main base of the memorial, which is approximately 1m high. Have a closer look at it.

1. What ‘things’ can you see within the base below the inscription, and what size is the largest ‘thing’?

2. From your answer to Q1, what rock is this memorial made from?

3. What parish was the memorial “A TOKEN OF GRATEFUL REMEMBERANCE FROM.…"?

4. If viewed from above, what shape does the base of the memorial have: a pentagon, a hexagon, a heptagon, or an octagon?

Please do not post photos of the memorial, but please feel free to post photos of yourself with the imposing St. Mary’s Church in the background.

Good luck!