Part of a series of EarthCaches and other types of caches that demonstrate how Geology and Forensics are often used together to explain features we find in rocks. This EarthCache is placed with the kind permission of The Royal Armouries, for which they are gratefully thanked.
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. Common examples include Granite, Gabbro, Basalt, and Obsidian.
2 – Sedimentary Rocks
- These form when older rocks have been weathered and eroded, then transported, and then deposited, usually in layers. 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).
- 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. The local ‘famous’ limestone in this area is ‘The Chalk’, a nearly pure-white deposit formed by calcareous mud about 60-80 million year ago being turned in to rock, preserving the marine creatures that could be found within it
- 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 crystallise or re-crystallise, depending on the original rock. Common examples include: Marble, Slate, Schist, and Gneiss (pronounced ‘nice’).
Fort Nelson was built in the 1860’s as part of a defensive chain around Portsmouth and its vital Royal Dockyard, which lies only 3.75 miles away. The Fort is now a Scheduled Ancient Monument. It covers nearly 19 acres and is owned and maintained by Hampshire County Council. Since 1995 it has been the home of ‘The Royal Armouries’. On display in their Museum of Artillery, part of the ‘National Collection of Arms and Armour’, are representative pieces of artillery from all around the world, covering every period of History. The Fort is free to enter.
The coordinates for this EarthCache takes the cacher underground.
I have given the Terrain Rating as ‘1’ due to the access to the GZ being via lifts (if required) in the Museum, then flat and smooth concrete and/or tarmac pathways. The underground passageways, comprising the same ‘pathway’ build, are artificially lit, and angle northwards (i.e. downwards as one moves deeper underground, but at no angle greater than 15o. However, it is ‘uphill’ when returning to the surface, so this should be born in mind if using/pushing a wheelchair or stroller. A torch will probably be useful but is not vital, as the tunnels are artificially lit, providing satisfactory but overly bright lights.
At the coordinates one will find themselves about 5m underground, in the area of the ‘Main Magazine’. Here the cacher will find two vaulted chambers that open off the north-south access tunnel (the tunnel being brick-lined from here to the Tunnel Entrance from the south). These rooms could hold 2,500 barrels of black powder. All metals fittings were non-ferrous to prevent sparking, and no naked lights were allowed. As one approaches the Main Magazine area, you will see the ‘By-Pass Tunnel’ curve away to the east, then re-join again to the north. The Main Tunnel then continues northward from where the By-Pass and Main Magazine meet – it is these tunnels the EarthCacher needs to study.
As usual with EarthCaches there is no physical cache.
To Log this EarthCache, please:
1 - study the tunnels and the main Magazine area
2 - then possibly do some research,
3 - then email or message me the answer to these questions:
I strongly recommend ‘saving’ this EarthCache before entering the Museum Buildings, and definitely before going underground, due to the lack of signal!
QUESTION 1: What is name of the white rock that makes the tunnel walls, and what percentage of the wall and ceiling surfaces does it comprise?
QUESTION 2: Within the white rock is another rock (‘Rock X’). What is name of this rock, and what percentage of the wall and ceiling surfaces does this comprise?
QUESTION 3: Describe the relationship of ‘Rock X’ within the white rock.
QUESTION 4: Look carefully at the bare rock walls. What fossils can you see, and what do these tell you about how the white rock and ‘Rock X’ were formed?
QUESTION 5: In the Main Magazine, the cacher will find black ‘shells’. How many are there, and what size are they?
QUESTION 6: What colour are the walls and ceilings of the Main Magazine, its immediate area, and the Main Tunnel to the south of here? Why do you think they were painted this colour?
Please email or message me your answers via the Message Centre.
Good luck! 