Chesil Beach Description Formation Pebbles Storms Chesil Home

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.

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. It can be distinguished from building stone as the air pockets are irregular in shape and position.

Building stone

There is a type of building block that closely resembles pumice stone and this can be found on the beach. It is usually lighter in colour and softer than true pumice stone. There are also some brick fragments on the beach from demolished buildings.

Cinders

Lumps of cinder are common along the Fleet side of Chesil Beach. Most are thought to come from  the days of steam ships when ships would discard cinders from the boilers. Some floated and came ashore on Chesil Beach. Being light they were transported over the beach top and came to rest on the Fleet side of the beach crest.

Crude oil conglomerates

A modern contribution to the beach is crude oil conglomerates. They originate from the late twentieth century when tankers would regularly flush their tanks while travelling down-Channel. The lumps of oil floated and eventually came ashore on Chesil, picking up small stones and pieces of plastic on the way. Since then they have hardened and can now be found in some numbers along the Fleet side of the ridge.

Others

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

Limestone pebble from the beach at Chiswell

Further information

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

Pumice stone from Chesil Beach

A crude oil conglomerate containing numerous pieces of plastic

A piece of cinder from Chesil Beach