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THE GEOLOGY OF JERSEY (Click here to see a basic geological map of the island)Millions of years ago Jersey was part of a huge volcano that stretched from what we now know as our island across to France. It's not surprising, therefore, that rocks formed as the result of volcanic activity form the largest proportion of the island's geology. |
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Broadly speaking our geological make-up can be split into 4 specific types: Granite: Granites are formed when magma (molten rock) is pushed upwards from the earth's core into overlying rocks. Unlike a volcanic eruption, the magma does not erupt through the surface but cools deep within the earth. Large deposits can be found on the north, south west and east of Jersey and these were formed between 550 and 420 million years ago. The granite here is an attractive pink shade and was commonly used in the past as a building material, some of it being exported to use on the Thames embankment. Shales: Shales and sandstones are re-cycled rocks: existing rocks are eroded by rivers or the sea to form sand and mud. These deposits are then compressed to form a new rock. The Jersey shales are the oldest rocks in the island, formed around 700 million years ago, and can be found in the south and west of the island. Conglomerates: Conglomerates are beds of pebbles, cemented together. These can be found in the north east of the island and are our youngest rock formations - formed around 400 million years ago. Mixed deposits of volcanic rocks: A large area of mixed volcanic rock deposits stretches across the island towards the east coast. Examples here are ignimbrite, rhyolite, andesite and diorite.
* It's well worth visiting the geological section of La Hougue Bie museum to see a more detailed map of the many types of rock deposited on the island.*Anyone looking for a detailed map to own, please contact me at my e.mail address below. |
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