The Magnesian limestone escarpment, looking north from Bowburn.
The village where I live is overlooked by the Magnesian limestone escarpment formed from a coral reef dating from the Permian era. On cold winter days I get a perverse pleasure from contemplating this escarpment and mentally transporting myself to a balmy tropical beach beside the Zechstein Sea, 250 million years ago, watching the trilobites scuttle around in the shallows.
The Magnesian limestone extends about 20 kilometres east from here, ending at the Durham coast where there is some classic limestone coastal scenery You may have encountered this coastline before as Easington, a few kilometres to the north, was the setting for the film Billy Elliot and the closing sequence of the 60s thriller Get Carter were also filmed here. Both of these films refer back to Durham’s mining heritage. Now, however, the pits have all closed and the area’s natural beauty is able to flourish once again. There are some unique limestone grassland communities associated with the Durham coast, with orchids and primroses abundant in the spring.
It was, however, far from spring-like when I visited last week, with a biting wind blowing in from the North Sea. The clear skies, however, gave some spectacular views. Looking north, I could see almost the entire Permian coastline, as far as the headland at Souter, just south of South Shields whereas in the other direction I could see the industrial sprawl of Teeside and, beyond it, the North York Moors south to Whitby. About 80 kilometres of coastland were on display from the beach at Blackhall.
Looking north along the coast at Blackhall Rocks on a cold February day.
My interest in Blackhall lies in the particular type of limestone that is found here. The technical term is the “Hesleden Dene biostrome” and, looking closely, I can see within it some finely laminated horizontal layers within the rock, each no more than a millimetre thick, that are formed from layers of filamentous blue-green algae, such as those we have seen in the River Ehen and elsewhere, albeit marine rather than freshwater, that gradually accumulated on the shallow bed of the tropical sea that I fondly dream about. They are often flat, as in the picture below, but sometimes form mounds and hummocks reminiscent of the stromatolites that I wrote about recently (see “The origins of life …”). The twenty kilometres I travelled from my home to Blackhall is also a journey back 250 million years, well before the age of the dinosaurs. Yet it is also a reminder of a yet more ancient world, that of the Precambrian where the earliest fossils of stromatolites have been found. That requires us to repeat the 250 million year journey to the Permian about six more times to take us back 1.5 billion years to the middle of the Precambrian.
Laminated strata of fossilised algae in the Hesleden Dene biostrome at Blackhall Rocks.
I’ve known about the fossil algae at Blackhall for a long time and they were even the subject matter for a piece of video art I produced whilst doing my Fine Art degree (fear not .. the file is far too large to consider uploading). Whilst searching the internet for information to refresh my memory I happened upon a resurrected online edition of The Vasculum. This was a local natural history journal produced by the Northern Naturalists Union, which thrived on contributions by both amateur and professional ecologists. During my time as a postgraduate student, Tom Dunn, the editor (and an enthusiastic lepidopterist) would prowl the corridors of the Botany and Zoology Departments at Durham making sure that we had all paid our subscriptions. I had thought that The Vasculum was one more victim of our gradual slide towards a culture of armchair naturalists so I was delighted to see that it is now thriving in a new, online format. Long may it last.
Birtle, M. (2012). The Permian landscape of the north-east coast in 2012. The Vasculum 97: 1-32.
See also: Blackhall Rocks (GCR ID: 3016) In: Volume 8: Marine Permian of England, Chapter 3: North-east England (Durham Province), Geological Conservation Review, JNCC