The blog of Alan Calder, novelist and poet. Author of 'The Stuart Agenda.'
Saturday, 28 July 2012
In one of my June posts I mentioned another visit to the famous Devonian fossil site at Achanarras Quarry in Caithness. I had earlier found a fossil of Dipterus, a four hundred million year old fish. Having been in the dark for all that time it is now fully exposed as the centre piece of an occasional table. Caithness Stone Industries, based at Spittal were able to cut out the fossil bearing stone and insert it into a polished piece of hard blue Caithness sandstone, creating a unique and very pleasing resting place for the fish.
On the same visit, although there are now very few stones left unsplit, I was surprised to find something that I though was a plant fossil because of the multi-branching tree like form. A quick e-mail to Prof Nigel Trewin at Aberdeen University confirmed that it wasn't a fossil, it was a dendrite. These are chemical deposits that crystallise in a dendritic habit from mineral containing fluids that seep between the sandstone planes. My sample, from the brassy colour is probably composed of iron sulphide, rather than the more common manganese based dendrites, which are black. The area around St Catherine's monastery in Sinai is famous for manganese based dendritic pyrolusites.