It's impossible to judge these things from photographs and I am sad that you would even consider this. Of course the wall behind and the cairns themselves are built from the same material - the local fieldstone. It is a soft variety of sandstone called 'Rotten Stone' or 'Mother Of Coal'. I will try and carefully jam one of the cupmark fossils into my scanner to produce an image, perhaps.

I've walked past these cairns several hundred times over the summer - that is the ultimate test maybe. I have been keeping their location sort-of quiet for fear of vandalisms. The young lambs jump on them - this is the main erosive force at present.