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Home > Landscape & Geology > Dorset Coast and Geology > Lulworth Area Formation- Types of Rock
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Current Geology
The exposed rocks in the area around Lulworth cove are made up of principally of 5 different types of sedimentary rocks (Chalk, Greensand, Wealden Bed, Purbeck Beds, Portland stone), formed between 150 and 65 million years ago. There is also a small amount of gault clay.
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Picture 1 of 12 -Lul...
The Portland stone was formed around 150 million years ago in the Late Jurassic period. It is a fine-grained. massive limestone, which was originally deposited in a calm shallow sea. Nodules of chert a hard flint like substance of almost pure silica help fortify the rock further. The rocks contai...
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Picture 2 of 12 -Lul...
The Portland stone is a hard limestone and forms a protective rampart to the Lulworth coastline. It is resistant to the battering of the waves, however where it has been breached bays (such as Lulworth cove) have formed where the softer rocks behind have been eroded away.
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Picture 3 of 12 -Lul...
The Purbeck beds are made of clays, shales, mudstone and limestone. They were deposited 147 million years ago. At the time of deposition this area lay in a large shallow low-lying lagoon. Minor variations caused water conditions to vary enormously between salty, brackish and freshwater, the clima...
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Picture 4 of 12 -Lul...
The projecting white bands are thin lagoonal limestones of early Cretaceous age alternating with lagoonal shales. They have had origins at various salinities. The Purbeck beds are made of clays, shales, mudstone and limestone. In places on the cliff and shore the clay layers of the upturned rocks ...
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Picture 6 of 12 -Lul...
The Purbeck beds are made of clays, shales, mudstone and limestone. They were deposited 147 million years ago. At the time of deposition this area lay in a large shallow low-lying lagoon. Minor variations caused water conditions to vary enormously between salty, brackish and freshwater, the clima...
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Picture 6 of 12 -Lul...
The layers of rocks give an indication of the ever-changing environmental conditions at the time of their formation. The early strata show a transition from marine to terrestrial. The cinder bed, for example, has the remains of echinoids (sea-urchins) in the rocks. These cannot survive in non-mari...
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Picture 6 of 12 -Lul...
After the Purbeck beds were laid down a series of earth movements changed the environment of deposition. A huge Wealden river carried sand, clay and grit sediments to a large freshwater lake inhabited by dinosaurs and early mammals. The rock layer is considerably thicker than both the Portland and ...
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Picture 7 of 12 -Lul...
The Wealden Beds are seen at Lulworth as low crumbly cliffs that are easily eroded by weather and sea their reddish-orange colour is caused by mineral iron staining the sand.
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Picture 8 of 12 -Lul...
The Wealden Beds are created from sands, marls, clays and grits deposited 140 million years ago. The Wealden beds are soft are very easily eroded.
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Picture 9 of 12 -Lul...
Deposited in a shallow sea, 125 million years ago, the greensand consists of layers of sandstone (there is a green staining due to the mineral glauconite, which is iron and potassium based). Although much better drained than the Wealden clay the rock is soft and susceptible to erosion. The rock c...
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Picture 10 of 12 -Lu...
Deposited in a shallow sea, 125 million years ago, the greensand consists of layers of sandstone (there is a green staining due to the mineral glauconite, which is iron and potassium based). Although much better drained than the Wealden clay the rock is soft and susceptible to erosion. The rock c...
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The white chalk is a deep layer of pure limestone. The youngest rock at Lulworth, being 97 million years old. The chalk was deposited very slowly in a clear shallow sea surrounded by a desert and consists of the remains of trillions of minute marine organisms.
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Although generally considered a soft rock, the chalk is surprisingly resistant to marine erosion and forms towering cliffs vertical along the coast. Some of the chalk contains bands of flint, which fortify the rock; flints are created in areas that formally contained sponge beds. The rock only cont...
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