War Memorial #1932 ~ Wanstead EarthCache

The Earth Science

If anyone has found many earth caches, most of this you've covered before, but because this war memorial shows so many different materials at a low level that's accessible by wheelchair, I'm aiming for a child-friendly accessible earth cache.

Sedimentary rocks are formed by the sediments of material that accumulate and consolidate into rock. There are three main forms of sedimentary rocks;

• Clastic sedimentary rocks like sandstone and breccia are formed from other rocks broken up into fragments by erosion;
• Organic sedimentary rocks, like coal or fossiliferous limestone, are derived from plant and animal remains;
• Chemical sedimentary rocks are formed by chemical process - e.g. rock salt layers from the evaporation of salt water.

Sedimentary rocks tend to have observable grains in their structure and sometimes obvious layers from their formation. They can also have obvious fossil inclusions, parts of shell or impressions of fossils. The colour depends on their chemical composition, limestones are white or creamy coloured from the calcium carbonate in their chemical composition, others are pink from iron content. They often feel gritty to the touch as if particles come away on your fingers.

Sedimentary rocks are laid down in layers, in some places significant layers. One of the more widely used limestones in the UK, Portland Stone, was laid down in a shallow sea, with dissolved calcium and carbonate ions of dissolved carbon dioxide in the water settling out as the water evaporates, combining with fragments of shells. This mixture accretes into ooliths, egg shaped pieces of calcium carbonate, gradually collecting and building into layers of rock. This means that the stone can contain many fossils that can often be seen on the surface, particularly if the stone is polished and used inside to prevent weathering. The Isle of Portland has been extensively quarried and the open quarries and jetties to ship the stone out are dramatic sights from the sea. Portland stone has been used in buildings in London as it is less subject to weathering than many other sedimentary rocks, but it is relatively easy to work as are most sedimentary rocks. Buckingham Palace, St Paul's Cathedral, the British Museum, parts of Paternoster Square and the church of St Mary the Virgin in Wanstead are all examples of buildings using Portland stone.

Igneous Rocks are formed when melted rock, magma, that originated from deep below the Earth's crust cools and solidifies. The size of crystals found in the rock depends on whether the rock cools underground - intrusive rocks - or above the surface - extrusive rocks. Igneous rocks are harder than sedimentary rocks, but that hardness makes them more difficult to work.

• Intrusive rocks have bigger crystals and form coarse-grained rocks such as gabbro and pegmatite;
• Extrusive rocks are formed from lava, erupted magma, which cools quickly creating fine-grained rocks such as rhyolite and basalt. These rocks are classified by how much silica they contain, which is not going to easy to observe at this location.

These rocks can look very crystalline, or just feel rough if extrusive igneous rock. They don't have the same powdery feel of sedimentary rocks.

These rocks were discarded pebbles near a lead mine and show the large crystals of an intrusive quartz formation.

Metamorphic Rocks are those that have been altered by intense heat or pressure. They can be formed from sedimentary rocks, igneous rocks or other metamorphic rocks. Contact metamorphism is when the rocks are changed by heat from igneous intrusion or lava flow. Regional metamorphism is where rocks are crushed in the middle of, for example, the formation of a mountain range. Examples of metamorphic rocks are marble, slate, schist and gneiss. Marble is formed from limestone rock, slate from shale. As the description of sedimentary rocks above suggests, these sedimentary rocks may have layers of other substances in their formation, These layers are what make the veins in marble.

Metamorphic rocks tend to be smooth to the touch. Marble and slate are familiar materials from their use in household surfaces and marble in sculptures. Marble Arch is covered with Carrera marble.

The War Memorial

The First World War memorial in Wanstead was designed by Newbury Abbot Trent and unveiled in 1922 by James Roll, a local dignitary at the time. The statue on top of the pedestal is that of Victory, modelled in bronze, crowned with a laurel wreath, wings outstretched, her right arm raised and her left hand holding a palm branch. The highest panel on the side of the memorial, naming those lost in World War 1, is of green marble with incised lettering.

The Tasks

There are several different kinds of stone used in the creation of this war memorial, all of the questions can be answered from ground level. The information is give that the higher panel is of green marble to discourage climbing on the monument.

Can you use your judgement to decide which kinds of stone have been used in the different sections? Please can you send the answers by message, by logging them when you claim the find. Claims without answers will be deleted.

1) The war memorial base is described as being of black granite in the listings, but in earth science terms, granite could be one of several igneous rocks: i.e. both the intrusive gabbro and extrusive basalt are granites. Also, unhelpfully, the base has a black coating on the sides, covering the rock. It is exposed on the top surface.

a) From your observations, do you think that the bottom plinth (the bottom stepped layers) is formed from intrusive or extrusive igneous rock?

b) Why do you think this material was used?

2) a) What sort of stone do you think was used for the pedestal (the tall main part of the monument)?

b) What evidence can you see that supports that idea?

c) Why do you think this material was used?

3) (a) What material do you believe is used for the panels for the names from WW2?

(b) What evidence suggests that this material was used?

4) Optional - include a photo of you or something identifiably yours at the war memorial in your log, without giving away any of the answers.