Any geologists out there?

Last week I took a recuperative break in Lyme Regis. Well known for it's unusual geology of course. Wandering on the beach I came across stuff like this:

I forgot to put a ruler next to it, but for scale the biggest hole is about 15mm.The 'stone' is quite soft and may be compressed mud - but how were the holes formed? Googling has so far failed me.

Robin

Just asked my brother (specialist in rock and fossils) And he came up with this.

the Jurassic Coast in Dorset – and lots of other U.K. locations as well. Many of these tunnels, burrows or borings have been made by small marine invertebrate animals such as certain species of bivalved molluscs, polychaete worms, and even sponges.

David

Piddock!

I have seen teredo marine worm holes in mahogany about that size or bigger.

Martin

Wrinkled rock-borers and piddocks!

Info: here.

Regards,

Phil

You can see rock on the IOW coast intertidal zone with holes like that with little red sea anemones at the bottom

It's an early bullet proof vest left over from the dino-wars. The fact that it's so full of holes and that there are no dinosaurs left are evidence that the early vests weren't very effective....

Have they finished "stabilising" the town?

I've seen rocks like this in a California river, small hard pebbles have worn the softer rock away by the agitation of the water passing over them over time.

Robin,

Those holes are remarkably round for a fossil, with well formed edges.

I suspect that it's something from the old town dump that slid down onto the beach many years ago. Somewhere there's someone looking for one of those.

Brian Bristoll.

Looks like a prehistoric twist drill holder to me! Some of the old fossils on here will no doubt confirm this?

Ian

Arf! Might have a use in the workshop then, hadn't thought of that. Some of the holes are indeed remarkably round, which made me think that there was some physical (eg bubbles in mud - but I couldn't see quite how that would work) rather than organic mechanism at work. But armed with the search term 'piddocks' further googling pretty much confirms that's how the holes were formed. Astonishing, I'd never have guessed that!

It turns out that the same question was asked in the New Scientist a couple of years ago. One of the replies runs thus:

Both shipworms and piddocks exude shell material to line their burrows and prevent them collapsing. The civil engineer Isambard Kingdom Brunel learned from this, and used the same strategy to successfully complete the first tunnel under the Thames in London.

The remnants of (presumably) exuded shell material are visible in my specimen. I wonder if it's true about Brunel though? I can believe it I suppose, he probably drew inspiration for his innovations from many sources.

Thanks for all your replies - I expected that someone here (or their brother ) would shed light.