By Bernie Bell
Last Sunday, Mike and I went for a walk along the Bay of Skaill. It was one of those days, when a stormy tide has washed the sand away, leaving big slabs of rock exposed. It gives a whole new aspect to Skaill Bay – I’m more used to it being a big sweep of sand, with pleasingly rounded stones in a bank at the top.
After a storm, when the sand is scoured away, the slabs of rock have the odd rounded stone scattered, almost placed, on them. They also have rock pools among them – it’s a very interesting time to clamber about on the rocks. We were doing just that, when we saw this…….
Seaweed sometimes leaves marks like that, but , if you wet them and rub them, they go away. We tried that, but the marks didn’t go away, so we thought it might be a fossil, and I took a picture of it, so that Mike could ask one of his colleagues about it. This is someone who started off as a palaeontologist, then morphed into a marine ecologist, so he might know, either way. And so it turned out to be.
His verdict on what happened, was that it’s not a fossil, but it is a mark made by a seaweed called Desmarestia ligulata , and what has probably happened is that a piece has lain undisturbed for long enough that the acid from it has caused a chemical change in the rock that has etched its shape more permanently than is usual. Possibly it was covered over with sand during the summer, protecting it from being moved, then both sand and seaweed have been swept away by the winter storms, leaving the seaweed’s ‘ghost’.
A fossil would have been of interest, laying there, all those ages, until certain conditions revealed it again, but, I think this is just as interesting, in a different way.
A seaweed ‘ghost’ – a bit of chemistry, a bit of natural history, an echo of one of Rebecca Marr’s photograms, where Rebecca places seaweed directly onto light sensitive paper, and exposes this to light. The seaweeds create their own image. Like, but not like, what had happened here.
And all there, on an Orkney beach.
We do have a picture of a fossil fish which we took at the right hand end of Skaill Bay, some months ago. That’s a generally more rocky area, and we were lucky enough to find this……………………..
And , by now, they will probably have both disappeared again – re-buried, or washed away by the waves. So it goes.