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A cache by Quenrelia - adopted from Loony Londo Send Message to Owner Message this owner
Hidden : 5/13/2010
4 out of 5
1 out of 5

Size: Size: other (other)

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Geocache Description:

This cache is about an igneous rock which is one of three types of rock igneous, sedimentary and metamorphic rock.

** **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 statute of Benjamin Disraeli (Lord Beaconsfield). He was a fascinating character but we are interested in the plinth on this occasion. The plinth is made of a very hard rock. It was formed when different types of rock melted and formed a new rock when the molten rock crystalised. It has a granular structure containing many grains. If you look closely you will see three different materials making up the stone. There is also a dark mark on the West Face of the plinth on the left hand side near the words "Earl Beaconsfield”. It is part of the original rock which did not melt when the rock was formed.

The current theory of how such a rock is formed is as follows. Below the surface of the earth on which we walk lies molten rock magna. Floating on this sea of magna are plates of solid rock. They are the tectonic plates which are in constant movement. Where the plates meet, one plate will slide on top of another plate, forcing it down into the sea of magna. The downward pressure causes some of the molten magna to swell up in bubbles and melt some of the rock above.

The molten rock under great pressure from the solid plate above cools slowly to form large crystals. Not all the original rock melts and fragments of it remain in the rock which gives a clue to how this rock formed. At a later date the newly formed crystals of rock are forced up and expand as they are under less pressure. This two stage process forms the rock forming the plinth. There are other theories but for the purpose of logging the rock you must answer the following five questions.

1) Name the type of stone

2) Describe the three materials making up the rock and if possible give their names though this is not essential

3) Give the name given by stone masons to the dark patch found in this rock or alternatively the scientific names for these patches of the original rock.

4) Look at the Dark Patch. Is the shape of it rounded or angular. Can you give a reason for its shape?

5) Look at five of the rectangular crystals in the stone. Measure their length, average their size and then state whether the rock is coarse, medium, or fine grained using the following scale: coarse crystals are over 5mm in length, medium crystals are between 1-5 mm in length , and fine crystal are less than 1mm in length .

To claim this earthcache as a find, please send me an email and tick the box to send yours too (rather than a message through GC) detailing the name of the cache in the title and the answers to the above five questions along with your caching name (eg Quenrelia). As the questions have changed since creation of cache, be sure to refresh the page so as to send the appropriate answers.

Photos of yourself and your GPS are encouraged although there is no requirement for you to do so should you wish not to. Please do not reveal the answers in your log!

Any log that does not meet the requirements will be deleted without further notice - please ensure you send out the answers prior to logging the cache, including the caching name of everyone in your party.

The information in this cache about the plinth is taken from Eric Robinson and Martin Litherland 's booklet "Holiday Geology Guide Westminster" published by the British Geological Survey but you do not need to read the leaflet to find the answers as the information to answer the questions can be found by looking at the stone and using the Internet

Good rock hunting!

I would like to thank Loony Londo for setting up this cache and helping so many of us understand what sometimes feels quite complex.


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Additional Hints (Decrypt)

Uvag bar: Gur fgbar vf znqr bs tenvaf juvpu fubhyq uryc lbh gb nafjre gur svefg dhrfgvba.

Uvag gjb: Gur anzr bs gur pnpur fubhyq uryc lbh jvgu dhrfgvba 2.

Uvag Guerr: Gur ebpx pbzrf sebz Fpbgynaq.

Decryption Key


(letter above equals below, and vice versa)



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

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Rendered From:Unknown
Coordinates are in the WGS84 datum

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