Portland Roach on the Cobb: Detail of the Portland Roach limestone blocks from The Cobb, Lyme Regis, Dorset, UK on the Jurassic Coast (1)

Fossils are not only found in the cliffs, the rocky ledges of the beaches, and the boulders strewn across the shore at Lyme Regis in Dorset. Even when you take a walk around the harbour, on the top of the massive sea defence known as The Cobb, there are fossils beneath your feet – but these shelly remains have come from further afield.

The Cobb is a great sinuous, almost organic-looking, sea wall enclosing a safe haven for boats. It is constructed from huge blocks of fossiliferous stone. You can easily see in the cut surfaces of the stone vast numbers of  bivalve and gastropod shells preserved as fossils and moulds within the rock. The blocks are Portland Roach, or Portland Admiralty Roach, which is a shelly oolitic limestone coming from the uppermost part of the Portland Stone Formation of the Upper Jurassic Period on the Isle of Portland. These big blocks lie above smaller slabs of Blue Lias argillaceous limestone from the local reefs. The Roach stone itself is characterised by the presence of moulds left by the long  pointed gastropod locally known as ‘The Portland Screw’ – Aptyxiella portlanica – that has something like a turret shell shape.

The large number of holes that riddle the Roach stone mean that it is not really suitable for building construction in the way that the famous Portland limestone is used. However, Roach is frequently used for seawalls and sea defences.

The Cobb has been in existance for many centuries but what is seen today is a reconstruction from 1820. I think that was the first time in its history that the blocks of stone were mortared together. Mortar is most visible between the stones at the landward end but towards the seaward end some extra measures have been introduced to reinforce the structure. It looks as if the patchwork of blocks have been curiously secured together with giant iron staples.

Portland Roach blocks on The Cobb: The upper surface of the curving sea defence known as The Cobb, at Lyme Regis, Dorset, UK on the Jurassic Coast (2) 

Portland Roach: Blocks of Portland Roach limestone with mortar in the sea defence known as The Cobb around the harbour at Lyme Regis, Dorset, UK on the Jurassic Coast (3) 

Fossil rock used for building: Fossil shells embedded in the Portland Roach stone used in the building of The Cobb around the harbour at Lyme Regis, Dorset, UK on the Jurassic Coast (4) 

Giant iron 'staples' securing the blocks of Portland Roach limestone on The Cobb at Lyme Regis, Dorset, UK on the Jurassic Coast (5)

Giant iron 'staples' securing the blocks of Portland Roach limestone on The Cobb at Lyme Regis, Dorset, UK on the Jurassic Coast (6)

View looking along the top of curving harbourside sea defence of The Cobb towards Monmouth Beach, at Lyme Regis, Dorset, UK, on the Jurassic Coast (7) 

Revision of a post first published 10 May 2010


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8 Replies to “Rock on The Cobb”

  1. This makes me think not only of the “young people…wild to see Lyme” but also THE FRENCH LIEUTENANT’S WOMAN, by John Fowles. It must have been unbelievably exciting for amateur geologists to realize what they were walking on back when the idea of evolution and the earth’s age was new.


  2. I am woefully ignorant of things literary, P.j. I have heard of the book and the film of The French Lieutenant’s Woman by John Fowles in which the Cobb features … but I am unfamiliar with your first quotation “young people..wild to see Lyme”. Can you tell me more? I agree with you that it must have been tremendously exciting for the first fossil hunters – and the tradition continues. Lyme Regis has just had a fossil festival in which Charles Darwin and a DoDo made an appearance.


  3. As I have just said to P.j. Grath, I don’t know much about fiction and I am unfamiliar with the characters in The French Lieutenant’s Woman – but a quick Google search indicated that she fell down some steps on The Cobb. As it happens, I did photograph three sets of steps when I was there and you can see where Louisa Musgrave fell if you look at tomorrow’s post!


  4. Just shows how my literary education is lacking!
    I have just written tomorrow’s post for you with pictures of the stone steps.


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