Images of patterns on the beach caused by wave action winnowing out lighter black sediments from the heavier yellow sand grains have been shown in earlier posts. Here are three microphotographs of the black sediments from a small sample that I scooped up on the shore at the time. Sorry there is no scale because I haven’t fathomed out how to include one in the images yet.
Hopefully these shots are clear enough to show that the numerous black particles are small fragments of waterlogged wood; shiny hard pieces of coal (coal dust); a few large pale seeds not yet identified; minute fragmented seashells such as mussels; and many white slender organic objects which I think are small fish rib bones but could be or include heart urchin spines. It was these bones that gave the dried sample in the petri dish an almost fibrous appearance. I am going to see if I can find someone from the world of archaeology who would be familiar with the analysis of this type of material – to see if I can get some more specific information about these black sediments from the beach at Rhossili in Gower.
The next stage of the walk from Hill End to Spaniard rocks saw an even greater reduction in the numbers of washed up starfish, and correspondingly greater concentrations of seashells in the strandlines, mostly empty shells of the bivalve Pharus legumen. The fine black detritus arranged itself in elaborate patterns mostly to do with the drainage of water back down the beach.
The sample of the fine dark particles that I took at the time, turns out to have a very interesting composition now I have had a chance to examine it under magnification back home. There is a fair proportion of small dark decaying wood fragments but most of the black material is composed of minute shiny hard particles of coal (what you might call coal dust). The coal is not difficult to account for since coal mining and its export from nearby docks was a major industry in the past. There are many ways the coal could have been accidentally deposited in the sea. Together with the coal dust there are various seeds that I am not able to identify and, most surprisingly of all, what seem to be myriads of delicate fish bones. In fact, so many small threadlike rib bones that the dried sample seemed to have a fibrous texture. Amazing.