London Marble Arch

Marble Arch is a 19th-century marble faced triumphal arch and a London landmark.

(More information further down. BUT first the earth lesson.)

Lets learn more about the Metamorphic Rocks and the Marble Stone:

Metamorphic Rocks

These rocks get their name from the Greek words ‘meta’ and ‘morph’, meaning ‘change of form’. Metamorphic rocks are produced by the alteration of pre-formed rocks by pressure, temperature and migrating fluids, often in environments deep in the Earth’s crust. Because of the severe conditions which rocks undergo during metamorphism, the original minerals may become unstable and change to maintain equilibrium with the new environment. This can involve changes in mineralogy (recrystallization of existing minerals or formation of new ones) and usually changes in texture from the original rock.

Three main types of metamorphism are recognized. Regional metamorphism results from mountain-building events with large scale folding and burial of pre-formed rocks. Contact metamorphism is produced by direct heating of rocks around an igneous intrusion, baking the surrounding country rocks. Dynamic metamorphism occurs where large scale faulting breaks and deforms rocks next to the fault.

Marble

Marble is a metamorphic rock, formed by the alteration of limestone under high temperature and/or high pressure. Marbles formed from pure calcite limestones are white, with a sugary texture, and they effervesce when tested with dilute (~10%) hydrochloric acid. Impurities in the limestone may lead to the formation of new minerals, giving the marble a variety of colours. Stonemasons often give the name marble to any rock that takes a good polish, but this is incorrect in geological terminology.

The worlds famous white marble comes from Carrara in the Italian Appenines where it has been quarried for two thousand years. It is probably the finest in the world for sculpture, and has been used by famous sculptors such as Donatello, Michelangelo and Canova for their masterpieces. The Taj Mahal in India is built of white marble from Makrana.

Colour: may be uniformly white and glistening, light brown or grey; also variegated with green, red or black.

Mineralogy: 95% calcite (CaCO₃) or dolomite Ca,Mg(CO₃)₂. Impurities may give rise to new minerals such as olivine.

Composition: calcareous.

Texture: medium to coarse grained, often showing a sugary texture.

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Questions

1. Answer the questions under by visiting the Coordinates.

A. Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. What can you say about the Marble at gz? And as Marble is formed from limestone, you often find fossils in these types of stones. Can any fossils be seen here? If so, what types of fossils? (crinoids/corals/brachiopods)

B. Why is the stone color (light/medium colored/dark)?

 C. From what you see at gz, what color is the Marble (white/brown/red/Green/Black)? And what is it that the impurities in the marble stone may give rise to?

D. How many % of calcite or dolomite would you guess is in this marble stone at gz?

E. What period of time does the displayed Marble come from?  (Use the diagram above from the cache text, and pick your answer from the right hand side, saying: Period.)

2. Take a photo of yourself, the group or your GPS when logging the cache.

Without revealing any answers!

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Marble Arch

History of Marble Arch

Marble Arch was built by the architect John Nash in 1828. The reliefs on either side are by Richard Westmacott and Edward Bailey. The grand statue of King George IV, which once sat atop the parapet, was moved to Trafalgar Square.

Nash based his design on the Constantine Arch in Rome, intending it to be the front gate of Buckingham Palace. It stood near the site of what is today the three bayed, central projection of the palace containing the well known balcony. Unfortunately the arch proved to be too narrow for the State Coach, and it was moved to its present position in 1851.

A memory of its former home still lingers on in local law… If you are feeling rebellious, then have a march through the central arch – as it is still technically illegal for a commoner to pass through the royal gate. Historically, only members of the Royal Family and the King's Troop, Royal Horse Artillery are permitted to pass through the arch; this happens only in ceremonial processions.

The area around Marble Arch today is rather less regal, as it was once the home of Tyburn Gallows. The original site is marked by a triangular plaque on the roadway.

Prisoners were dragged up from Newgate Prison and stood upon a wooden cart. The horses were then whipped and ran away, leaving them to dangle from a noose. An estimated 50,000 people were put to death between 1300 and 1783.

The arch gives its name to the vicinity of its site, particularly, the southern portion of Edgware Road and also to the nearby underground station.