Peat ‘pebbles’ with piddock holes

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Peat 'pebble' with bore holes made by piddock bivalve molluscs, on the strandline at Whiteford Sands, Gower, West Glamorgan (1)

These pebbles look like rock but when you pick them up they are light and obviously organic. They are made of ancient peat that underlies the sandy beach at Whiteford Sands. The peat is about 10,000 years old and occurs in layers alternating with clay and interspersed with pebbles. These strata are being eroded away by the action of the waves. You can sometimes see the deposits outcropping during low tide at Whiteford Point – just beyond the Whiteford Lighthouse.

The pieces that break away from the seaward edge of the peat layer can be a metre or more across and these large lumps occur as islands dotted sparsely across the vast expanse of wet sand. Much smaller pieces often wash up on the strandline. The edges are rough and uneven when the peat has recently broken away. Smoother, more rounded, pieces are the result of peat fragments rolling around in the sea over a length of time. It is possible to see preserved leaves and stems incorporated into the peat. These are clues to the past environment. Apparently, no-one has yet studied in depth either these plant remains or the submerged forest timber.

Intriguingly, you can frequently find neat circular holes drilled into the peat. These  boreholes have been made by boring bivalved molluscs -although they look regular enough in shape to be man-made. I have written in earlier posts about soft rock and pebbles with holes made by sea creatures. Also shells with holes made by boring bivalves. So it would seem that peat is an additional suitable substrate in which molluscs like piddocks can live equally well.

One of the pieces of  peat I picked up on my last visit still had the empty shell of the mollusc in one of the borings. I don’t know whether the shells are ancient or modern. I have not seen any live molluscs in these peat colonies; or in any of the nearby colonies to be found in the clay deposits either. Only empty shells so far.

The shells are very fragile and usually break when you try to extract them. I am going to try and get some decent specimens so that I can make a definitive identification. And I will keep searching for live animals as this will show that at least some of the boreholes in the peat and clay on this Gower beach (and its neighbours like Broughton Bay) are modern. In theory, you could radio-carbon date the shells (for example, this has been done for archaeological oyster shells from Poole in Dorset) but that costs money.  

Piddock bore holes in a peat pebble: Close-up of rounded and water-worn piece of peat with holes excavated by bivalve molluscs such as piddocks, from Whiteford Sands, Gower, West Glamorgan (2)

Shells of boring mollusc in peat pebble: Detail of peat block showing borings and paired piddock shells in situ, Whiteford Sands, Gower, West Glamorgan (3)

Peat pebble with embedded leaves: Smoothed and rounded lump of ancient peat showing embedded leaves and other vegetable remains, on the strandline at Whiteford Sands, Gower, West Glamorgan (4)

Peat layers beneath a sandy beach: Alternating layers or strata of peat, pebbles, and clay, eroding out at the water's edge on Whiteford Point, Gower, West Glamorgan (5)

Peat and clay on the beach at Whiteford Sands: View looking up the shore at Whiteford Point, Gower, West Glamorgan, over rapidly eroding relatively recent geological deposits of peat and clay (6)

Small lumps of peat braking away from a layer on the beach: Small, cobble sized pieces breaking away from the seaward edge of the clay and peat strata that normally lie beneath the sand at Whiteford Point, Gower, West Glamorgan (7)

Revision of a post first published 22 January 2010


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14 Replies to “Peat ‘pebbles’ with piddock holes”

  1. Hi ref peat pebbles erm where do I start.I was walking from st Edmunds head Hunstanton back to the town along the beach I saw many peat pebbles large and small with said holes but one I found had what seem to be a large vertibra next to it or had come out of it.As it was as black as the peat itself is this unusual ???????? Regards Jeff


  2. Hi, Jeff. Sounds like you might have made an interesting find. Did you take a photograph of the vertebra thing or take it home with you? You can find all sorts of things in peat. I usually find leaves, twigs, and branches. I have also found layers of seashells such as cockles and mussels. However, in some places in the UK like Cheshire, they have found ancient buried people (Lindow Man), and in Denmark they have found quite a few human remains (the Bog People – Tollund Man). I believe the area around Hunstanton is well known for the finding the bones of animals (mammals) that are now extinct but which were around during the Ice Ages. So you might well have found something interesting from the peat on the beach!


  3. Hi Jessica I have try to send photos of vertebra in peat found on Hunstanton beach but as yet with no luck.My pad is having problems I think with your email address so it tells me.
    But I will try to think of some other way later. Regards jeff Great blog by the way


  4. I look forward to seeing the photographs of the vertebra when they get through. I have been receiving e-mails without problem today so the difficulty might lie perhaps with the large size of the photograph files. Perhaps try sending one picture at a time – the address is –


  5. Hello… just found your blog having come home with piddock shells pulled our of the peat on Borth Beach at low water. Thank you. Great source of information and beautifully written. The images at the top of each page are fascinating – is there a label hidden anywhere so readers can find out what they’re looking at?


  6. Thank you for your comments, Rachael. I’m glad you found the piddocks information useful. About the header photos that change with each new page, I hadn’t thought to attach a description to those but it is a good idea. I’ll try and do that some time. All the other photographs have a description attached to them when loaded, and if you click to enlarge the image you may see that description – but apologies because it doesn’t always appear. I know it can be found if I have displayed the images in a gallery, and for more recent postings. However, the description doesn’t appear for earlier posts – I think because I changed the “theme” a year or so ago.


  7. I am send some really great pictures of stone found in Ohio creeks by my husband. They all are rocks with holes.


  8. I found a multitude of these in Widbey Island Washington State. I make jewelry with them because I am allergic to all metals. I use leather straps for the chain. My line is called “Earth Jewelry” I am hoping to make another trip there to collect more. Are there any beaches in Florida that might have these type of rocks?


  9. Hi, Cindy. Sounds very creative and practical to make jewellery from peat pebbles with piddocks holes to suit wearers with sensitive skin. I am fairly certain that you would be able to find similar pebbles on Florida beaches. As I live in England and am unfamiliar with the Florida coast, I first Googled the words ” peat deposits Florida beaches” and the search yielded a great number of articles about peat onshore and offshore along the Florida coastline that had been drowned thousands of years ago during sea level rises. Then I Googled “piddocks Florida beaches” as it is the piddocks bivalves that make most of the large holes in the peat and other fairly soft rocks. From this search it seems that there are at least four commonly found piddocks in that area. These include the Atlantic Mud Piddock (Barnea truncata), Wedge Piddock (Martesia cuneiformis), Striate Piddock (Martesia striata), and Atlantic Woodeater (Xylophaga atlantica).

    I think you would have a good chance of finding peat pebbles with holes on some Florida beaches; and you could perhaps find out which are the most promising locations for them by looking at the published articles on submerged peat deposits as found on Google.

    Hope this has helped.


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