Geological Forensics 10 - H.M. Royal Navy Dockyard EarthCache

Part of a series of caches that demonstrate how Geology and Forensics are often used to together to explain features we find in rocks, especially in urban settings.

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

The placing of this EarthCache has been allowed with the permission of the National Museum of the Royal Navy, for which their permission is gratefully acknowledged.

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 - formed when magma cools slowly underground over millions of years, granites typically have contain larger crystals, giving some quite pretty textures, and have a general paler colour.
• Basalt – formed by magma being extruded as lava at the Earth’s surface from a volcano. These typically cool very quickly, giving us igneous rocks which contain small crystals. They are darker in colour than granite.
• Gabbro – formed in a similar way to granite, but of the same composition as basalt, gabbros have larger crystals but are very dark in nature.
• Obsidian – formed in the same way as basalt, these cool even more rapidly, forming microscopic crystals, often 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, giving the rock a ‘lined’ appearance, often with some larger minerals starting to form, these themselves showing signs of deformation, giving some of them a ‘rolled snowball’-type appearance.
• Gneiss (pronounced ‘nice’) – formed when schist is further deformed, causing the already-elongated minerals to grow even larger still. These crystals can then often become bands of colour within the rock, these themselves also being deformed, taking on the appearance of wavy lines of differing colour to the ‘main’ mass of crystals that surround it

As usual with EarthCaches there is no physical cache.

To Log this EarthCache, you have to complete 2 tasks:

Task 1

Please go to the coordinates. You will note that these are inside the world-famous Portsmouth Historic Dockyard, which itself is part of H.M. Royal Naval Dockyard. This is a working naval base, but you are allowed in (during opening hours) to view the floor for free. If you wish to view the ships and/or the exhibits and museums, you will probably have to pay a fee (NOTE - ocasionally there are large 'special events' held within the Dockyard. If so, there may be a compulsory entrance fee to gain entrance to the Dockyard - I advise checking their website before planning to tackle this EarthCache, just in case!). The Historic Dockyard is open 10:00 – 17:30 most days of the year.

At the coordinates you will find yourself standing on the upper section of a concrete slipway, which is bounded by a metal fence (that stop people from gaining access to the sea). Stand with your back to the fence (i.e. back to both the sea and H.M.S. Warrior), and look at the road surface. You will note that as you look at the surface, from the concrete under your feet, looking ENE along to ‘Porters Garden’ and the start of ‘College Road’, the materials used to build the road surface vary not only in age, but also in their composition.

Assuming the concrete is the 1^st first ‘type of road rock’, moving away towards Porters Garden gives you the ‘last section of road rock’.

The task is to identify (using the above information), the correct order of 12 sets of ‘road rocks’, starting underneath your feet, and ending 20m across the road, at the raised area which is denoted by a two-step high 4m x 4m square-shaped area.

The three choices are:

CHOICE 1

1. Under my feet = Concrete
2. Kerb = garnet mica schist
3. Cobbles = pale granite
4. Kerb = garnet mica schist
5. Cobbles = pale granite
6. Track-way for the wheels of carts, once pulled by horses = gabbro and basalt
7. Cobbles = Cornish granite
8. Other part of the track-way for the wheels of carts = gabbro and basalt
9. Cobbles = Cornish granite
10. Kerb = garnet mica schist
11. Cobbles = pale granite
12. The 2 step-high square-shaped raised 4m x 4m area = a grey limestone

CHOICE 2

1. Under my feet = Concrete
2. Kerb = pale granite
3. Cobbles = pale granite
4. Kerb = pale granite
5. Cobbles = pale granite
6. Track-way for the wheels of carts, once pulled by horses = Cornish granite
7. Cobbles = gabbro and basalt
8. Other part of the track-way for the wheels of carts = Cornish granite
9. Cobbles = gabbro and basalt
10. Kerb = pale granite
11. Cobbles = pale granite
12. The 2 step-high square-shaped raised 4m x 4m area = granite

CHOICE 3

1. Under my feet = Concrete
2. Kerb = pale granite
3. Cobbles = pale granite
4. Kerb = pale granite
5. Cobbles = pale granite
6. Track-way for the wheels of carts, once pulled by horses = limestone
7. Cobbles = gabbro and basalt
8. Other part of the track-way for the wheels of carts = limestone
9. Cobbles = gabbro and basalt
10. Kerb = pale granite
11. Cobbles = pale granite
12. The 2 step-high square-shaped raised 4m x 4m area = granite

Task 2

Look at the statue at Waypoint 1.

Please tell me:

1. Who is the statue dedicated to?
2. What is the rock type the plinth is made from?

TO CLAIM THIS EARTHCACHE - Please email or message me the answers to the above Tasks.

Please do not post photos of the ‘road rocks’ or the statue, but please do post photos of yourself and the many views and/or historic vessels and/or other vessels that you will see from this important spot.

Good luck!