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War Memorial #990 ~ London - Siege of Malta EarthCache

Hidden : 01/18/2020
2.5 out of 5
1 out of 5

Size: Size:   other (other)

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Geocache Description:

This EarthCache is located within an area frequently patrolled by Police (and/or Beefeaters). Please avoid acting suspiciously whilst completing the Tasks, and, if challenged, please freely explain about geocaching. It may be worth pointing out that it is not a physical box you are looking for, but are simply studying the rocks visible to everyone.

War Memorial #990 ~ London - Siege of Malta

The posted coordinates will take you to an interesting memorial (both historically and geologically) to the Malta Siege during World War II. The memorial is formed out of a block of Maltese stone. If you would like to see more information relating to the Siege of Malta, please read the information panels on the memorial. This earthcache aims to teach about the geology of Malta. Update: as of the 1st February 2020 the cache has been updated and is now in the War Memorial national series.

The geology of Malta

The archipelago of Malta consists of almost 100% sedimentary rock. There are two different ages of rock present on the island, the rarer and older rock being from the Oligocene period (34-23 million years ago) and the newer rocks being from the Miocene period (23-5 million years ago). There are four different types of stone on the island, shown below:

Coralline limestone comes in two varieties (lower and upper), but the most common variety, Upper Coralline limestone, was formed 7-5 million years ago. It is a hard limestone which can be pale grey or light yellow in colour. It forms the top layer of the Maltese formation and is the easiest to extract. The famous Azure Window in Malta was formed of this type of limestone. Pieces of upper corraline limestone are susceptible to easy weathering.

Globigerina limestone is a common limestone found all across Malta and was formed 23-14 million years ago. It is a golden-coloured soft limestone which often contains many fossils (commonly of the Globigerina plankton, giving it its name) and is usually gold-coloured, however can take on a rosy colour when exposed to air. Some rocks can erode and weather very easily and it is known for constituting the majority of building material in Malta. It almost exclusively weathers in a 'honeycomb' pattern.

Blue clay mudstone is a mudstone found on the Maltese archipelago and was formed 15-10 million years ago. It is often a blue/grey colour and shows major thickness variations. It was formed in a deepwater environment and can be found towards the northwest of the archipelago. It allows the capture of rainfall and the formation of aquifers.

Above: Malta's famous 'Azure Window' (now sadly collapsed) was formed of Coralline limestone.


The weathering of rocks is quite simply the breaking down of the stone at the Earth's surface, by action of rainwater, extremes of temperature, or biological activity. It doesn't involve the removal of rock material. There are two main types of weathering:

Physical weathering is caused by physical processes such as changes in temperature, freezing and thawing, and the effects of wind, rain and waves. An example of physical weathering is freeze-thaw weathering, where water expands slightly when it freezes to form ice. The formation of ice can break rocks, as if water gets into a crack into the rock, it freezes into ice, expanding the crack and making it bigger. This process then repeats itself with the crack in the rock getting bigger every time.

Chemical weathering occurs when the minerals within the rocks are chemically altered. In the process of carbonation, rainwater and carbon dioxide in the atmosphere combine to form carbonic acid. This means all rainwater is slightly acidic. This carbonic acid dissolves minerals within the rock, weakening the structure and resulting in damage and wear. On statues or monuments this can also result in the appearnce of staining on the surface.

Questions to answer

Please read the above text before you attempt to answer the following questions.

1. Go to the above coordinates where you will find the memorial to the Siege of Malta. Describe the main memorial block's appearance (overall colour, texture, and any other relevant points).

2. Given your answer to Q1 and the information in the description, what type of Maltese stone do you deduce the main memorial to be made out of, and how many millions of years ago was it formed?

3. Examine the main memorial block again, but this time looking for signs of weathering. Has the memorial been stained? Has it been affected by physical weathering, chemical weathering, or both? You need to bear in mind the location of the memorial in relativity to its surroundings.

Feel free to take photos however please don't upload any of the memorial. Thanks!

When you have answered all the questions, either message me through the website by clicking "Message this owner" at the top of this page or email me here, quoting the GC code.

Feel free to log this cache as soon as you have sent your answers however please note if I haven't received a message/email within 7 days of your log I will have no choice but to delete your log.

Additional Hints (Decrypt)

Nf jvgu nyy RneguPnpurf, gurer vf ab pnpur pbagnvare ng gur cbfgrq pbbeqvangrf - ernq gur qrfpevcgvba naq nafjre gur dhrfgvbaf.

Decryption Key


(letter above equals below, and vice versa)