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?

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