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## Ostra antigua

A cache by Loony Londo Message this owner
Hidden : 06/11/2010
Difficulty:
Terrain:

Size:  (other)

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### Geocache Description:

The cache is about sedimentary rocks and a large fossil.

# **This cache is located within an area frequently patrolled by Police. Please avoid acting suspiciously whilst searching for it, and if challenged, explain about geocaching**

You are standing by a bronze statue of King Charles I. The statue is placed on a stone base which is has been there for many years and as a result it is heavily eroded.

If you look to the North you will see the National Gallery extension where you will see some newly quarried examples of this stone. It is white and smooth unlike the stone making up the base of the statue.

The degree of erosion of this stone gives you a means of estimating how long ago the stone was quarried. The stone formed when small particles of a salt crystallised out of solution and formed tiny egg like grains which over time became a smooth rock which can be cut in any directions to form neat blocks.

However at the time this rock was forming there were creatures living in the sea. and when they died their remains fell into the sea floor and were incorporated into the stone. These remains are harder than the stone forming the base so as that stone erodes the fossils slowly emerge. This is explains why fossils are constantly appearing as the rocks containing the fossils are eroding away.

On the NorthWest corner of the stone plinth you will see a large fossil.

To log this cache answer the following questions:

1) Name the type of stone .

2) Describe the large fossil and measure its size.

3) Name the type of creature which was fossilised.

4) When the plinth was first placed in position, the surface would have been smooth but over time the surface would have eroded away exposing the large fossil. Measure how far the large fossil protrudes from the surface and include this figure in your answer. Given that this stone erodes at the rate of approximately two milimetres a century, how long do you estimate this stone has been here exposed to the elements?

If you have sent me your replies to the questions on the Web page, there is no need to wait for a reply from me before logging your finds.

I try to reply to all emails but as I have five Central London Earthcache, I receive about 10 emails a day which is something like 3,500 emails a year. Unfortunately l recently was rather behind with replying but I have now managed to catch up with my replies. If you have not received a reply, please email me.

 I have earned GSA's highest level:

This cache now has more than 250 favorite points .There is an Earthcache Challenge Cache "I ♥ Earthcaches Challenge" http://coord.info/GC5647Y which requires you to find an Earthcache with more than 250 favourite points so if you have found this cache you may equailfy to log a find for GC5647Y

Thanks to every one who gave this cache a favorite point..

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Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)

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### 3,578 Logged Visits

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**Warning! Spoilers may be included in the descriptions or links.