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Nature Trail 3

Limestone/geography of Mendip
3

Limestone is a sedimentary rock formed from calcium rich deposits. Much of the limestone here on Mendip was formed as part of a shallow, warm sea, around 350 million years ago, from the bodies of the creatures and plants which lived in that sea. There is a fossil coral here in this rockface, can you spot it?

As the soft sediment, shells and other materials settles to the sea floor, it is covered by further layers of other materials, and over millions of years is transformed, through a process called diagenesis, into the limestone we see today.

But how did a sea floor become a mountain which has now eroded to form hills? Over 250million years ago the collision of two continents caused the ‘uplifting’ of this once sea floor, buckling the stone and causing it to become a mountain. In some places on Mendip, including the old quarry here at the Mendip Activity Centre where we do our climbing sessions, you can see the sedimentary layers which have been shifted from horizontal to vertical!

When water is contaminated with carbon dioxide (acid rain) it is capable of dissolving limestone. This has happened throughout the history of Mendip, due to volcanic activity elsewhere on earth and through other natural processes. This dissolving of the limestone has created the many miles of caves that can be found beneath Mendip, would you like to go and see these caves?

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