Patterned Sand 8 – 14: Naturally formed patterns of black sediment on yellow sand were photographed on the beach at Rhossili Bay, Gower, in April 2017. The black sediments were mainly composed of minute pieces of rotten wood, coal dust, and miniscule fish bones, with a small proportion of seeds. The images have been digitally colour-enhanced to emphasise the patterns of this natural abstract art.
Patterned Sand 1-7 – Naturally formed patterns of black sediment on yellow sand were photographed on the beach at Rhossili Bay, Gower, in April 2017. The black sediments were mainly composed of minute pieces of rotten wood, coal dust, and miniscule fish bones, with a small proportion of seeds. The images have been digitally colour-enhanced to emphasise the patterns of this wonderful natural abstract art.
The entire coastline north and south of Louisbourg on Cape Breton Island in Nova Scotia, Canada, is composed of Neoproterozoic volcanic rocks dating back 575 million years. A few hundred metres north of the Louisbourg Lighthouse along the Trail to Morning Star Cove and Gun Landing Cove, lies an area of seashore that offers the chance to take a close-up look at the compositions and natural patterns in rock made of pyroclastic breccia.
Pyroclastic literally means ‘fire-broken’ and is used to describe volcanic rocks made up of fragmented pieces that are normally the result of an explosive volcanic event. Clasts are pieces of broken down rock. According to the Oxford Dictionary of Earth Sciences edited by Michael Allaby (ISBN 978-0-19-921194-4) “breccia is a coarse clastic sedimentary rock, the constituent clasts of which are angular. Breccia literally means rubble and implies a rock deposited very close to the source area. The term may also be applied to angular volcanic rocks from a volcanic vent.
Rock of a similar type of origin, although not identical, has been used by the sculptor Emily Young in the creation of the carved heads that were recently on display on Neo Bankside in London. Stillness Born of History II is described as being made of “onyx with volcanic pyroclastic brecchia”.
Beautifully textured and patterned onyx with volcanic pyroclastic breccia has been used by the famous sculptor Emily Young to create this fabulous head called Stillness Born of History II displayed (courtesy of Bowman Sculpture) at Neo Bankside in London, England, just south of the Tate Modern Gallery. Pyroclastic breccia is composed of fine-grained volcanic ash, pumice, and rock fragments larger than 2.5 inches (63.5 mm). When the fragments are smaller than this, the rock is called tuff.
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.
As I walked further along the beach from Hill End to Spaniard Rocks, I realised that there were maybe four or five strandlines lying parallel to each other and to the water line. Each line of mainly organic debris was slightly different in its constituents. Similarly, there were changes in the make up and proportions of the animal and plant debris in the strandlines in a linear way as I walked from south to north along the shore. The starfish became less numerous and the numbers of bivalve molluscs and their shells increased,
Most noticeable was the way in which the darker particle component of the strandlines became separated out on the up-shore side of the lines, and formed patterns contrasting with the yellow sand on which it lay. Sometimes there were branching lines of clear spaces, like rivulets running through the black stuff. Sometimes, the black pieces followed and echoed the shallow ripple marks in the sand – either as parallel lines or cross-hatching designs full of beautiful natural abstract compositions. In other places, small obstacles such as seashells had formed little dams to impede the flow of lighter, darker, material as the water that carried it swashed and backwashed over the beach, and this had created distinctive patterns as the water flowed around the barriers.
I was curious about what made up the fine black material responsible for the patterns. I took some samples to look at under the microscope when I got home.