Scratching the surface

This episode initially takes us from Chesters on the Wall to Hexham. South of the Wall but very much a gateway and one with some important recycled Roman rocks. Then back to close to the Wall at Fallowfield before jumping back south to Roman Corbridge – Coria or sometimes Corstopitum. The geology will be as diverse as the geography. From the rocks that made millstones to a cavalryman's tombstone, 

Transcript

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Episode six Scratching the Surface First, I think I ought to explain the time gap between the last episode and this one. There are a few reasons. Had some talks to prepare and to give, then family came to visit, and lastly my wife Jill managed to break her wrist, so it's been a bit busy lately. This episode initially takes us from Chesters on the Wall to Hexham. That's south of the wall but very much a gateway to it, and one with some important recycled Roman rocks. Then we head back close to the wall at Fallerfield, before dropping back south to Roman Corbridge, Korea, or sometimes Costopitan. The geology will be as diverse as the geography, from the rocks that made millstones to a cavalry man's tombstone. Grain was a vital part of the diet of a Roman soldier. The large granaries at forts like Arbeir and Corbridge are clear evidence of that. To process grain into food, the soldiers needed rock, millstones, or known as quirns. The earliest types were saddle shaped, one stone rocked over another to crush the grain. More efficient were rotary querns, initially just two stone discs with a handle, which became more sophisticated and diverse. As well as hand tools, the Roman army also built mills driven by water and animals. Water mills have been rarely found along the frontier. But one was discovered at Halt Whistleburn near Corfield's Quarry, its wheel race cut into Windsill Bedrock. There are water channels at Willeford Bridge and Chesters Bridge too, and they may be evidence of water mills. You could understand the need to mechanize. Grinding by hand would take one man half a day to produce enough flour to feed eight men in his barrack room. Sandstone hard enough to make millstones is common throughout the local Carboniferous and Permian bedrock, and many querns can be found at Roman sites along the wall that are made of it. The particle size of the sandstone used varies, seems to matter less than their durability. Pinpointing where the sandstone to make the querns comes from is as challenging as tracing Hadrian's wall stone itself. Sandstone is such a ubiquitous rock, and there can be as much variation in the composition in one quarry as there is across kilometres of outcrop. Sandstone with sand particles that are well cemented together made good millstones. Volcanic rocks, lavas with lots of small gas bubbles, called vesicles, were even better. They self sharpened and left fewer stone particles in the flower. Querns made of lava have often been found along the frontier, and while similar rocks exist in Britain, these millstones are foreign imports. They were quarried from very young, that's less than one million years old, volcanic rocks at Mayen, in the Eiffel region of Germany, and they can be traced because their geochemical and petrological signature is relatively unique. The superior qualities of these quirns meant they were a valued and traded item before Roman times, and they were exported across the empire. The legions prized Mayan querns and carried them on their campaigns. Mayan quirns dominate Roman finds in Tonga and in Belgium, so it is no surprise that they were used by the Tungrian cohorts posted to Britain. Both lava and sandstone quernstones turn up regularly in excavations in Roman sites. A beehive quern, assumed to be German, was found very recently in the wall excavation at Drumbruff, but while it was an igneous rock, it wasn't a continental lava. It was a granitic rock, most probably an erratic from the criffled albiti granite across the Solway. Querns are often found in foundations and wells, sometimes deliberately broken, a ritual act that predates the Romans. Chester's Fort Museum at Cholliford is a great place to see the whole range from geologically youthful imports to our local ancient stones. We are in Hexham, and inside its abbey, one with a Saxon crypt, like the abbey, built with many Roman stones. But there is a very spectacular Roman stone just inside the entrance, beside the night stairs. Much of what we know about the Romans is from their prolific carvings in stone, sculpture, inscriptions, and even graffiti. While there are Roman literary sources, there are few and they're often second hand. The writing tablets of Vinderlander have been a revelation, but they remain a rare insight. Roman inscriptions and carvings in stone shed light on so many things. Centurial stones tell us who built sections of the wall. Altars, statues and tombstones record the gods they worshipped, their leaders and the lives of their dead. Not least their graffiti carved in bedrock reminds us that in many ways people in the past are just the same as people today. In Hexham Abbey there is a Roman tombstone. It is large, about two point seven meters tall. It was found face down under the Abbey floor in eighteen eighty one, and like the stones in the Saxon crypt, was robbed from nearby Roman ruins, almost certainly those at Corbridge. It shows a soldier riding a horse over the figure of a naked man. The carving quality is typical of the frontier. The makers were craftsmen, not artists, and their raw material was roughed sandstone, not Carrara marble. The tombstone, its inscriptions and symbolism, tell us about the soldier and his times. His Roman name was Flavinus, but it may not have been his birth name. He was a first century cavalryman, a standard bearer in the Ala Petriana. This was a unit originated in Gaul, which would become one of the elite regiments in the Roman army. He wears a tunic and a cloak, a helmet with a plume and a torque, a metal ring around his neck. His weapon is a sword. He had joined the army when he was eighteen, and was twenty five when he died. The carving has a recurring theme domination of a cowering enemy, an ancient Britain, perhaps. The memorial is large. Did Flavinus make regular contributions to a burial fund to pay for it? Like virtually all the monuments along the frontier, this one is carved from northern rock. After almost two thousand years of both reverence and neglect, its surface is worn smooth. There are few macro sedimentological clues, but on the left face are vertical lines. Bedding planes probably. This fits. Such a tall stone would usually be quarried parallel to the horizontal depositional plane of the rock. So it we can say that the tombstone is now perpendicular to its original orientation. The true colour and characteristics of the sandstone are hard to discern. Superficially it has a pale grey brown patina, and it looks local, that's Carboniferous. But on the right hand face, very small chips reveal red sandstone. Could it have been carved from the Triassic or Permian rocks of Cumbria? A more detailed analysis of the rock's mineral particles would tell her whether it was from younger Cumbrian stone, but the ubiquitous nature of these sandstones would, as ever, likely frustrate attempts to uniquely connect it to the precise place from where it was quarried. On a footpath, just northeast of the hamlet of Fallfield, and off a minor road south of the military road, is a flat outcrop of Carboniferous sandstone with little or no soil or grass covering it. It looks as if it has been scraped clean by a massive road planing machine. This and the scratches on it make it a very special bit of sandstone that has helped geologists understand what our landscape has experienced. The flat surface of the sandstone is evidence that this area was eroded by a thick, fast moving ice sheet only twenty thousand years ago. The scratches that glaciers and ice sheets make are called glacial stri. They show the direction of movement, generally west north west to east southeast. Some of the scratches here appear to accentuate sedimentary features in the sandstone. The ice sheet was moving from Scotland and Cumbria across Northumberland, and as it did so it scraped, bulldozed and carried billions of tons of rock, clay and sand with it. Stones and pebbles at the base of the moving ice literally sandpapered the bedrock beneath and gouged grooves into it. This is pasture land, with only thin soil. But look for pineapple weed growing in the joints of the bedrock. It smells like pineapple. Head a few meters south and east and you'll come to a very old quarry, one that was once Roman. How do we know that? The quarries opened by the Romans to build their linear frontier were numerous and widespread. But the only sure way to prove a quarry is Roman, is if their carvings remain. Stone extraction took place for centuries afterwards, and that, plus a landscape change in erosion, usually destroys evidence of earlier working. The quarry at Fallafield Fell, appropriately known as Written Crag, is seven hundred meters south of the wall in a carboniferous sandstone unit with a consistently thick top bed. As its name suggests, it had an inscribed rock, moved to Chester's Museum in nineteen thirty four. It says Petra Flevi Carantini Flavinus Carantinus, a Roman quarryman, left his name in the rock. All around Fallerfield are other quarries, working different sandstones, their deposition separated in time from the Fallerfield stone by tens to hundreds of thousands of years. To unequivocally and precisely trace where Roman wall stone came from is an almost impossible challenge. Why is it so impossible? The answer lies in how the rocks that provide the building stone originated, the conditions when they were deposited, their paleo environment. In the eastern two thirds of the frontier, the bedrock is Carboniferous sandstone, mostly made of quartz grains with some feldspar and mica. Three hundred and thirty million years ago, these rocks were billions of tons of sand in braided channels of large rivers flowing from a mountain chain in the far north. Over twenty million years the environment cycled repeatedly. River channels gave way to deltas, then lagoons, beaches and seas. These transitions left behind huge thicknesses of sand and other sediments that were constantly being redistributed. The outcome is billions of tons of rock that are rarely unique. Head west and forward in time to the Triassic Age, around 250 million years ago. The red sandstones that characterize this era and the western sector were a product of completely different environments. Those environments were deserts with shallow, transient rivers and lakes. These conditions also persisted over enormous spans of time and produced hundreds of meters of thickness of fine to medium grained red sand bees sandstone. This is another rock that is virtually impossible to provenance with any precision or certainty. Geoscientists have tried, analyzing both Carboniferous and Triassic rocks microscopically and geochemically, and simulating past environments. That's called paleogeographic reconstruction. Only where there is exceptional archaeological control and the potential sediment sources are very local and distinct, has it been possible to suggest the source of the Roman stones with any confidence? The frustrating outcome is that the best we can do is conclude that most of the standard building stones of the wall in the east came from quarries as near to the wall as possible. In the west, where bedrock is concealed by glacial deposits, the legions had to search out more distant outcrops. They were in the gorges of the Gelt, the Earthing, and the River Eden. But the environments these sandstones were deposited in were largely the same, and as a result, the rocks are too. We're in Correa, or sometimes Causopitum. Corbridge Roman town. We're here to see a Roman road, the Staingate. Sometimes its line is obvious on the ground. Sometimes modern roads follow its course, but mostly the Staingate is no more than a dotted line on an ordinance survey map. Literally the stone road, the Staingate runs for forty one Roman miles, that's sixty one kilometers between the towns of Corbridge and Carlisle. Stainegate is not its Roman name, it's medieval, but it describes well what it's made of. Most excavations of the road were done more than seventy years ago, at Corbridge, at Wallack just west of the North Tyne, and near Vinderlander and Haltwistle. In 1956 and 2022, water main trenches intercepted the road west of Newbrugh, near settling stones. Apart from a lack of marginal ditches, the Stainate is regarded as a classic Roman road. It often has sandstone kerbstones, and between them layers of rounded cobbles or broken angular sandstone and occasionally limestone and sometimes clay. Sandy gravel makes up the top wearing course and can be interbedded with other layers. It has been measured at almost seven point five meters wide and half a meter high in places. The materials used for its construction, especially the limestone, point to local geological sources. Roman Corbridge is the eastern terminus of the road and its junction with Deer Street. Korea is a very well preserved Roman town, with elegant buildings and monumental granaries. A good section of the road is visible as the main east west street, which runs past these buildings. The exposed surface is gravel from the river Tyne, cobbles of carboniferous sandstone, with a few glacial erratics of Silurian and Ordovician metamorphic and volcanic rocks. You may not be able to see the material the road is made of elsewhere, but it is sometimes visible in the landscape as a low linear mound with a noticeable camber. It used to have milestones, but today only one and a stump survive, in a field northeast of Vindalanda, and the fragment a Roman mile up the modern road to the west. The date the stain gate was built is disputed. Some think of it in Agricola's time, soon after the Romans moved into northern England around seventy AD. Others argue that it was constructed under Trajan's rule twenty years later, because the course changes to connect pre existing forts and fortlets along its length. It links places like Nether Denton, Throp and Old Church Brampton, rather than taking a direct route over higher, easier ground. Whatever its date, the road is still viewed as effectively marking the frontier of the Roman Empire until Hadrian built his wall in AD one hundred two. The Stainate stayed in use throughout Hadrian's reign, and when the next emperor, Antoninus Pius, moved the frontier north to Scotland, it remained a routeway. It was a highway until the end of the Empire, and in places it still is today. Well, if I hadn't marched you in and out of the Tyne Valley, and you'd been walking the Hadrian's Wall Trail, you'd have definitely noticed how much easier the walking had got. We left the windsill with its ups and downs a while back, and now the trail goes across more gentle carboniferous sedimentary rock country, hills and dales, not ridges and gaps. The final episode of this series is next, and we are off to the far east. But we will be starting well south of the wall in Lanchester before we head to the finishing line at Arbea and South Shields.