War Memorial #2090 ~ Furnace EarthCache

This EarthCache will take you to the War Memorial, at the centre of Furnace.

The purpose of this EarthCache will help you learn about Xenoliths and how they are formed.

Igneous rocks form when molten rock originating from deep within the earth’s crust cools (either below the surface as an intrusion e.g. granite, or above the surface as an extrusion e.g. basalt lava). The resulting igneous rock is composed of interlocking crystals, the size of which depends on the time taken for the molten rock to cool. If the molten rock cooled rapidly, the crystals are small (such as in felsite), if it cooled slowly (such as granite) the crystals will be larger. A common stone of the latter type is granite – due to the large crystal size in granite it is a very aesthetically pleasing rock. It is also very resistant to weathering and as such is found in many forms, in buildings, bridges, harbours and frequently for memorials as here.

A xenolith is an inclusion in the magma which formed the igneous rock and quite often it is part of the existing country rock into which the magma was forced. Due to this, xenoliths can be of varying sizes and can be quite different to the surrounding rock. Here we will look at the differing sizes of xenoliths found in the memorial and the coping stones of the wall around the memorial area.

As you are facing the War Memorial, please go up the steps and look at the left face of the stone that holds the names of the men killed in the First World War. About two thirds of the way up the stone, near the joint with the stones behind, you will find a group of 4 xenoliths. Look at the largest of the four.

Question 1: What is the colour and size (top to bottom) of this xenolith?

Now, please go back down the steps and around to the footpath behind the memorial.

Looking at the coping stones along the top of the wall around the memorial, you will notice that these are a different rock to the memorial. These are felsite, quarried locally.

Question 2: How do the crystals of the felsite differ from the crystals in the granite and why is this?

Looking at the coping stones, you should notice that the xenoliths here are quite different to the xenolith you studied in the granite. The image below should help you distinguish between lichens ON the rock and xenoliths IN the rock.

Question 3: Where are the xenoliths generally located within the coping stones (towards the top, in the middle, or towards the bottom)?

Looking at the coping stones behind the memorial, you will find one with a very large xenolith that has it's longest dimension at about 20 degrees from the horizontal (7th stone from the right hand end of the wall as you are facing the back of the memorial).

Question 4: Approximately how long is this xenolith and how many times longer is it than the xenolith from question 1?

Question 5: Please include a photograph in your log showing the FRONT of the memorial and including yourself or a personal item.

Answers to questions 1-4 should be sent by the message centre or email. Please DO NOT include the answers in your log.

Please send your answers BEFORE logging the cache. You do not need to wait for a reply, but if there is a problem, I will let you know.

ANY LOGS ENTERED WITHOUT ANSWERS BEING SENT WITHIN TWO WEEKS WILL BE DELETED.