I was out doing a little beachcombing yesterday and came across these
There were quite a few of them scattered amongst the weed along the intertidal zone. My best guess is that these marks are caused by limpets, possibly aided by wave action. It got me thinking about the cups that I’d been shown at Barraglom on the Isle of Lewis by the wonderful Margaret Curtis.
I’ve also read of similar small shoreside cups being used as bait mortars. The problem I have with this is that the cups I’ve seen are quite small and would probably not be very good as mortars, plus, why would you need so many? one mortar should suffice. Larger cups or basins yes but perhaps not the little fellas.
So basically all I want to do is throw these limpet marks plus a little erosion into the arena as another possible cause of cupmarks in the intertidal zone. Of course this theory would probably only work with sedimentary rocks. The rock in my picture is a Jurassic mudstone.