Chesil Beach

Pebbles

 

Removal of pebbles

Pebbles have been removed from Chesil for commercial puposes for much of the last century. A small amount was removed from near Chiswell, possibly amounting to 10,000 tonnes. A much larger amount was removed from the area between Abbotsbury and West Bay, possibly as much as 1.1 million tonnes.

This commercial extraction has now ceased and even casual removal of pebbles is discouraged to assist the long term survival of the beach.

Chesil Beach is made up almost entirely of pebbles of various rock types. The only exception is in the north-west section of the beach from West Bexington to West Bay where there is some fine gravel and coarse sand overlaying the lower levels of the beach near the tide line. The pebbles are graded in size from fist-sized near Portland to pea-sized at West Bay.

The types of pebble that can be found are:

Flint
Flint originates from the chalk beds. They include the slightly brownish pebbles, most of the medium grey pebbles and also the less well- rounded pebbles. They are extremely hard, harder than most steels.

Chert
The chert pebbles are also extremely hard and originate from the upper greensand beds. They are often fairly clear and translucent with a pink or bluish tinge.

Quartzite
Quartzite pebbles originate from around Buddleigh Salterton and are discoidal pebbles coloured red, purple "liver-coloured", or white.

Granite
Granite is occasionally found on Chesil Beach. It can be identified by the coarse grain size, the pink or white feldspar, the quartz of glassy grey appearance, and the black mafic minerals, normally mica and/or hornblende. These pebbles probably originated from further west on the south-west peninsula or may have come from the ballast of ships wrecked on the beach..

Porphyry
These pebbles most probably come from the Permian breccia in Dawlish, Devon. They are similar to granite in appearance, but the crystal structure is rather different. They are comparatively rare on Chesil Beach.

Tourmalised rock
Pebbles of hard black, finely granular material are common. Somewhat irregular pebble of vein quartz, stained yellowish, and tourmalinised slate, all sheared and partially brecciated. The pebbles are usually irregular in shape as the tourmaline is quite brittle.

Pebble size

pebbles

Pumice stone
Pumice stone from Chesil Beach

Breccia
A breccia is a rock of angular fragments. Only breccias that have been cemented strongly in hard silica can survive on Chesil Beach.

Portland stone
At Chiswell there are some limestone pebbles originating from the local Portland and Purbeck stone formations.

Kimmeridge oil shale
There is evidence that there was once an outcrop of oil shale on the back of Chesil Beach near Victoria Square on Portland. Pieces of shale can still be found on the beach and probably come from an outcrop under the sea off Chiswell.

Fossils
These are mostly found around Burton Bradstock and originate from the local cliffs.

Magnetite
This is believed to originate from the cargos of ships wrecked on Chesil Beach. The major concentration is near Abbotsbury and is believed to come from the SS Dorothea.

Peat
Pieces of peat can be found on Chesil Beach, particularly after storms. It comes from outcrops below the low tide level. It is mostly found at Chiswell and in an area around the tank defences at Abbotsbury

Pumice stone
Pieces of pumice stone are sometimes found washed up on the beach. Pumice is lava foam from volcanoes and contains sufficient air pockets to float. The stones on Chesil almost certainly came from volcanoes in the Caribbean Sea or central America. The colour varies from dark grey to almost white. They can be recognised by the large number of air pockets and that they are very light.

Others
Also found on Chesil Beach are Jasper, Agate, and Madrepores, but these are all very rare.

Limestone pebble
Limestone pebble at Chiswell
 

Further information
For a more detailed discussion of the pebbles that make up Chesil Beach visit Ian West's excellent website at Southampton University.

 

 

Last updated 20/3/2008

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