The Tees - from the moors to the coast

This is a journey from moors above the middle reaches of the River Tees near Barnard Castle to its mouth where it empties into Hartlepool Bay. Along the way the plan is to look at some prehistoric rock art at Barningham, celebrate the merits of sand and gravel and a hear a cautionary tale about flood risk, revisit the salt deposits of Teesside and in Hartlepool Bay hear about some graphic evidence of times when our coastline was very different 

Transcript

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Episode 2 The Tees From the Moors to the Coast This is a journey from the moors above the middle reaches of the river Tees near Barnard Castle to its mouth, where it empties into Hartleypool Bay. Along the way the plan is to look at some prehistoric rock art at Barningham, celebrate the merits of sand and gravel, and hear a cautionary tale about flood risk, revisit the salt deposits at Teeside, and in Hartlepool Bay hear about some graphic evidence of times when our coastline was very different. South of Barnard Castle and close to the Durham North Yorkshire boundary is Barningham Moor. A thin and incomplete veneer of glacial clay and near and far travelled stones covers the bedrock. A series of repeating and almost horizontal layers of carboniferous sandstone, shale and limestone. Several flat blocks of sandstone peep through the vegetation, detached pieces of bedrock which probably haven't moved very far. But it's not the geology of these rocks that's significant here. It's the marks and carvings that cover their surfaces, Neolithic and Bronze Age rock art. While carvings, cup and ring and groove markings are common and have been well documented in neighbouring Northumberland, there are few recorded in Durham, and some of the more spectacular ones here were discovered less than twenty years ago. Why these carvings are here and what they might mean are the subject of much debate amongst those with professional and amateur interests in prehistoric rock art. Lots of theories have been put forward, from the sublime to the ridiculous. Many of the carvings are at the margins of uplands, overlooking fertile ground below. Others are close to ancient roots. Some have been used in later circles and barrows. Some people who have studied them for decades believe we may be missing the point in looking for meaning, in their patterns, at least any meaning that twentieth century society can comprehend, and that they are part of a deeper spiritual relationship between ancient peoples and their landscape. Rock art is one of the many areas where geology and archaeology meet, and there would undoubtedly be benefits in the two domains working together more. Many carbons are plainly made by human hand, while many other rocks have unquestionably been shaped and sculpted by natural processes. But the origin of some marks on rocks is less clear. Were they caused by the scraping of ice sheets or thousands of years of weathering of natural layers and joints, or were they crafted by ancient people? Could it be that some are a combination of both? Perhaps to early societies, the shapes created by nature were art forms too, something they may have chosen to imitate and augment. We continue downstream, and to a bridge over the river Tees at Pierce Bridge, a place that used to have a Roman river crossing, but first a bit of promotion for an unsung geological hero. I suppose I'm saying this because I spent the first part of my geological career with the British Geological Survey doing what were technically called mineral resource assessments, but most people would know it as surveying sand and gravel. Mention geology, and I guess most of us think volcanoes, earthquakes and dinosaurs. Sand and gravel will probably not get a look in. But they are still bits of rock, and without them our lives would be pretty uncomfortable. The cement and concrete that builds our homes and infrastructure depends on sand and gravel. Sand makes the glass in your windows, the abrasives in your sandpaper, and it's in its bricks, paint and ceramics. Each of the valleys of the Tees, Tyne and Weir has ribbons of sand, gravel and silt and clay beside and beneath them. Gaze at the floodplain and terraces of the river Tees from Pierce Bridge. These deposits, sometimes in excess of fifteen hundred meters wide and ten meters thick, have been carried down by the river since the end of the last glaciation, fifteen thousand years ago, at first by huge amounts of meltwater as the ice sheets were retreating. As well as being beautiful natural assets, rivers and their sand and gravel have another, more menacing relevance to us. In quieter times today the river slowly shifts sand and silt along its bed, but when it floods, the water easily moves cobbles and boulders too, something which happened more often until Cowgreen Reservoir was built. Floods probably destroyed the first wooden Roman bridge which took Diaz Street across the Tees, and later unstoppable movements of the river meant that part of the second stone bridge were left as a causeway. Extreme weather events are forecast to become more common as the effects of climate change are felt, and many river valleys across the country will experience increasingly frequent floods. What is it that connects the man who played a key role in creating the nation of Canada? Smelly baths loved by Georgians and Victorians, Durham Jail, and the subsiding ground in Darlington. Well the answers are rock. Gypsum, hydrated calcium sulfate, CA SO four two H two O deposited between layers of mud in a shallow sea that evaporated frequently and in the arid climate of the Permian two hundred and fifty million years ago. In 1789, workmen employed by Mr John Lambton were boring a hole in search of coal on the bank of the river Tees, just west of Middleton Warro. After twenty two meters of red rock, they were shocked to find warmish water that smelled of rotten eggs gushing from the hole. The workmen claimed the water cured their rheumatism and skin complaints, and by seventeen ninety seven, after the medical men of the time had confirmed the health benefits of these sulfur rich waters, a bathhouse had been built, to complete to compete with the spas of Croft and Harrogate. People would come not only to bathe in the water, but to drink it too, and soon more accommodation was needed. Dinsdale Spa Hotel was built in eighteen twenty nine by the grandson of Mr Lambton, none other than John George Lambton, first Earl of Durham, Governor General of British North America in eighteen thirty eight, a politician and a diplomat. He was often known as Radical Jack, and in Canada as Lord Durham. He is renowned for his contribution to the establishment of their country and the assimilation of the French Canadians. Sadly, the Dinsdale Mansion designed by the architect Ignatius Bononomie, who also built the first bridge on the Stockton to Darlington Railway and Durham Jail, didn't generate enough business, and it was sold on in eighteen forty four. The link between the spa and the subsiding ground? The circulating groundwater has dissolved the highly soluble gypsum to produce sulfate rich spa water, with hydrogen sulfide causing the rotten egg smell. Those rock layers under Dinsdale slope up gently westwards, and gypsum beds up to forty meters thick lie beneath the rocks and the glacial clays here, at Croft and south and east of Darlington. When the gypsum dissolves the rocks above cave in, and that can cause subsidence at the ground surface, and sometimes damage to buildings and infrastructure. But back to health, and something that is genuinely beneficial, a walk along the Teesdale Way beside the river, past the old spar and through the peaceful scenery of this part of the Tees Valley. Those of you who've been listening to the previous episodes of this podcast may well have heard the tale about Teeside before, but industrial sites like this don't get a lot of coverage in geological guides, and as I thought it was an important stop on our journey down the Tees, I've included it, so you can either fast forward now for a couple of minutes, or if you'd like to hear it again, here goes. Without the rocks that hide deep beneath the ground surface, Teeside would be a very different place. The heavily industrialized land to the north of the Tees estuary is covered by a veneer of man made fill, which sits on soft tidal deposits of sand, silt and mud and glacial clays. Beneath those are two hundred and forty million year old sandstones and mudstones, and deeper beneath those are limestones that contain thick layers of anhydrite and halite. Two hundred and fifty five million years ago, these minerals were salt in a warm sea that extended from Durham to Warsaw. The level and extent of this primeval sea, called the Zechstein, fluctuated regularly, so the environment changed from open seas 300 meters deep to reefs and coastal shallow lagoons and desert plains. It was the evaporation of highly saline water at the western margin of that ancient sea that produced the layers of salts deep below Teeside and all along the Durham coast. Anhydrite, calcium sulfate, CASO4, contains 24% sulfur. Sulfur is a mineral crucial in the manufacture of chemicals and fertilizer. In 1926, Imperial Chemical Industries opened a mine at Billingham to extract it. The shaft was 260 meters deep, and the mine ultimately excavated around 320 kilometers of galleries and roadways. The mine closed in 1978, but the extensive underground chambers which remain have since attracted controversial proposals for the storage of waste, including low-level nuclear material and fly ash. A little further east, around 350 meters beneath Greatham, Salt Orm and Port Clarence are the deposits of halite, common salt, sodium chloride, NACL. They were originally extracted by uncontrolled brine pumping, but that caused subsidence at the ground surface. Controlled brine pumping was introduced, but in places that brought problems of salt contamination of groundwater resources in the overlying rocks. Brine pumping moved deeper and further east towards seal sands and used better methods of extraction. Since the 1950s, some of the cavities created have been used to store gases, including methane, nitrogen and hydrogen. Today, cavities within the salt for natural gas storage are specially designed and engineered. There's both irony and symmetry that it was a prehistoric natural sea that evaporated more than two hundred and fifty million years ago that brought the industry that caused the substance that enlarged the wetlands that today give a home to rich wildlife. Imagine it's seven thousand years ago. You're standing looking out over Hartleypole Bay, but instead of the grey North Sea there's a green woodland, and beyond that Fenland and Salt Marsh. Red deer forage in the glades, and Stone Age hunters stalk them. Fact or fiction? It's fact. The last glaciation and the subsequent melting had a profound effect on sea levels everywhere. The ice sheets had locked up enormous quantities of the world's water and lowered sea levels by as much as 120 meters below those today. The weight of the ice had also depressed the land, and so when the climate began to warm around 15,000 years ago, the release of ice pressure allowed the land to rebound. The melting of the ice discharged huge amounts of water into the seas and oceans, raising their level. These opposing changes didn't happen equally everywhere, nor did they happen at the same time. For geologists, geographers, and archaeologists, sea level fluctuations and their consequences for landscapes and for human history are a fertile area of research. And of course, they are acutely relevant as climate change has made this a very public and vital topic. But what's the hard evidence for these events? And for the forests and hunters in the bay. Every few years, when the tide is low, it reveals layers of peat and tree trunks. Found with them are pieces of worked flint, bones and antlers of deer. Submerged forests like these are often exposed around Britain's coast, in Northumberland and Cumbria too, and even dredged up in the middle of the North Sea. Analysis of the different types of pollen grains in these layers not only shows how the vegetation changed over time, from scrubby birch and alder, oak and elm to grassland, fenland and salt marsh, but when pollen analyses are pieced together, they provide a sequence that can be used in combination with radiocarbonages to date the organic remains and sediments. In 1972 there was a more spectacular find in the Pete of the Bay, human bones and the skull. Near the skeleton were worked flints. The bones have been dated at around 4,600 years old from the Neolithic or New Stone Age period. While this is an era defined by settling down and farming, it seems our prehistoric ancestors continued, just as we do today, to exploit the rich resources of our coastal environment. That's our geological journey down the river Tees over. If this river trip appealed, then the next one will be taken in places along the river Tyne. That river has its source not so far from that of the river Tees, but takes a northern, not an eastern course, leastways not until it reaches Holtwistle. So when you next log on, we'll be close to that source, south of a place called Garrigill near Alston, and deep in lead mining country.