The 'Carboniferous' is a geological period that covers the time span 359 to299 million years ago.
During this period Wales and Anglesey lay in the Southern Tropics. They were covered in warm, shallow Tropical seas full of abundant marine life.
Limestone was formed and deposited here at this time. Limestone contains calcite. Many invertebrate (no backbone) animals take calcite from the sea water and use it to build their shells or skeletons. When they die these shells are deposited as a sediment. Over time this is built up and compacted to form the hard limestone we see today. The limestone has moved from the Southern Tropics to here by the gradual movement of the outer crust of the earth called 'Plate Tectonics'
In the quarry you can see fossilised examples of all these sea creatures. You can see crinoids(sea lilles) as round base circles which is what is left of the stem. There are also colonial corals as compacted oval shapes (about 4 would fit on a pound coin). Look out for shell shaped brachiopods too.
If you turn and look inland you will see the limestone has a layer of red,silty, clay deposit containing numerous stones on top of it. This is 'Boulder clay' which was deposited here at the end of the last Ice Age. As the Ice sheet advanced it picked up mud and stones. When it retreated these were left behind.
To log this cache please email me the answers to the following questions;
1.The gps takes you to three limestone boulders. One is shaped like a triangular prism. Measure the diameter of the largest cicular fossil on this boulder.What sort of fossil do you think it is?
2. What type of rock is limestone? Igneous, Metamorphic or Sedimentary?
3.Look inland. Measure the depth of the boulder clay overlying the limestone by eye.
4.How many years ago did the Ice sheet retreat and leave this boulder clay.
5. Take a picture of yourself or your gps by another fossil rich boulder in the quarry (optional)
TAKE CARE AT ALL TIMES CLIFFS CAN BE DANGEROUS
If you want to further your geological studies we can recommend the Geomon centre at Amlwch and all their geological trails.