Wheal Martyn - Forming Granite

Most of what is now the British Isles was once covered by sea, upon the bed of which vast deposits of mud and silt collected.

In time their accumulated weight caused them to become compressed and hardened, converting them from loose sediments into highly cleavable forms of rock - the slates and shales which abound on the coasts of Cornwall and Devon to this day.

While the sediments were being laid down, vast land masses were drifting towards each other on a slow but inexorable collision course. The pressure generated caused the seabed to fracture, then fold – a process accompanied by intense subterranean activity that forced masses of molten rock upwards.

Between 290 and 270 million years ago the rock cooled into granite, a mixture of quarz, feldspar and mica. Today it forms the rocky backbone of the South West of England and is exposed in the Scilly Isles, Land’s End, Carnmenelis, Hensbarrow near St Austell, Bodmin Moor and Dartmoor.

To find out more about the formation of igneous rocks, such as granite, click on this link: -http://www.lgfl.net/dbmaterial/web/learning%20objects/ls/Year%203%20Science%20Rocks/lo2/