‘Cold cases’: land-scape puzzles on the Solway shore

“Mr Cash went to Beckfoot … the submerged forest was not visible and I regret to say the residents he inquired from had not even heard of it”. So wrote Brian Blake in his 1955 book The Solway Firth, which is illustrated by black-and-white photographs taken by J. Allen Cash. Fortunately, Mr Blake himself did find the forest later, and was “delighted with [his] luck” when he walked South from Silloth.

I first went to look for the forest back in 2004, and regularly found the stumps and roots of the ancient trees in roughly the same area of the shore near Beckfoot for many years. But it was not just the trees that made this forest area special: as I wrote back in 2004,

“the patches of black are like shadows along the sharp edges of channels in the sand. Walk down towards them, and the shadows resolve themselves into banks of peat. Poke them with your toe and feel how dense and sodden they are, smoothed by the friction of waves and sand. Walk on them and feel their sponginess. And gradually you will become aware that the dark organic mass is not only peat, but supports here a horizontal tree-trunk, or there a stump that radiates roots. Wander around and you will find trunks and branches, single and entangled, embedded in the peat and sand; and erect stumps, 20-30 cms high, their tops flattened as though cut by a chainsaw. The wood is still fibrous, soft and dark; you can crumble it and tease it apart, as though it were any rotting log in a woodland. But the difference is that this woodland thrived about 8000 years ago.”

The trees had died, their roots waterlogged as by a beaver-dam, their bodies gradually preserved as the sphagnum mosses grew ever upwards in the wet climate of the time, and compressed into acidic, anaerobic peat.

The forest and peat could be seen for more than a decade, but a few years ago during a sequence of winter storms, the peat was thrashed and fragmented by the waves, the wet and fragile wood vanished, and nothing remained visible of the woodland that had stretched across that earlier Solway Plain. But that patch had been just a small area: underneath the new and ever-changing profile of the mid-shore near Beckfoot – where shingle had been swept away, rocky scaurs (relics of glacial deposits) had been exposed, and sand had been piled in sessile waves and tiny ripples – the horizon containing the forest and peat and clay would still be present. It was a comfort to know that this evidence of the formation and changing development of the turbulent Solway Firth was still there – but hidden, from sight and perhaps from memory.

Vanished forest: shingle, sand-waves and a distant rocky scaur

January 2020

So, in January this year, after weeks of strong north-westerly winds and storm surges and Spring tides, I went down to Beckfoot again – wondering, hoping, that the secret of the submerged trees might once more have been revealed. The shore looked so different from the previous autumn that I was failing to find my usual ‘markers’. The cloud was low and the air was grey, and across the Firth Scotland had (very sensibly) taken leave of the Union and was no longer to be seen. A mixed flock of gulls sat and preened near the water, keeping a silent watch on my movements, and I apologised as thirty or more oystercatchers failed to hold their nerve and rose up in a flock, trilling with indignation.

I zig-zagged between the the tidelines, hoping to find ‘treasures’ like goose barnacles attached to flotsam, but the long mounds of tangled wrack and twigs were too tightly woven together by the waves. Dark shapes ahead were merely small boulders and rounded pebbles of a newly-exposed scaur.

Looking up to watch a curlew come gliding over the dunes, its outspread wings motionless as it let itself be carried by the wind towards the distant water, I saw that, higher up the shore towards the battered dune faces, there were smooth dark plates of … something. Not peat, as I had expected, but sheets of heart-stoppingly slippery, grey clay: the same type of clay that in the earlier exposures had lain beneath the peat layer that had preserved the forest. Had the peat been broken up and washed away, or was this one of those places where salt- or fresh-water had temporarily inundated the peat bog? Perhaps there had been a meeting of sea and river water, where the suspended sediment had flocculated and fallen – or perhaps the sea had broken through a barrier and washed out clay that had been deposited at the bottom of a still, small lake?

The clay’s surface was speckled with embedded fragments of wood – and there was a tree-stump with radiating roots; there were some fallen branches or perhaps more roots, half-buried in the clay. And more stumps, sticking up defiantly despite their age.

Intriguingly, the surface of the clay was pock-marked with tiny holes, the entrances to burrows. I broke off a piece and found the burrows had been filled in with yellowish sand.

November 2020

So much has happened – and not happened – during this year. One dramatic event happened on the Allonby shore, a short distance West of Beckfoot, during the high spring tides and storms of November. This wild weather broke open the dunes at Allonby to reveal a band of glistening clay at least one metre thick; the clay’s surface was patterned with bright brown deposits of iron salts, and black fragments of embedded vegetation decorated the smooth horizontal plates. (On a later walk I saw similar torn and decaying fragments of seaweed and twigs decorating the edge of a shallow pool, washed in and then dropped by the leaving tide.)

At the north end of this band of clay, a dark headland of peat jutted onto the shore. It was speckled with sand, and twigs and pieces of small branches were embedded – but these seemed more like collected flotsam rather than the remains of growing trees. A piece of what looked like black paper projected from deep within a broken edge and, picking at it, I was puzzled to find that it was a partly-exposed ‘mermaid’s purse’, the empty egg-case of a thornback ray. Nearby, the surface of one area of peat was coated in a hard crust of red-stained sand.

It’s like a detective story, a very cold case, with a complicated time-line. From the time the glaciers melted, about 10,000 years ago, until the present day, the levels of the sea – the Firth – relative to the land, have changed many times. You can see it most obviously where lines of pebbles sandwiched by layers of sand are exposed in the dunes – these are ‘raised beaches’ that show the different levels of the shore over time.

The height of each incursion doesn’t mark a simple water-line along the shore, for there would have been hollows and sandbanks, that either kept out or trapped the water: along the shore today you cross undulating sand-waves, find your way interrupted by water-filled channels, and discover that the former course of a beck across the shore has been changed by newly-banked shingle. Marine débris sinks in the still water, layering its patterns onto the settled sediment.

Sandwaves

The patterns of newly-exposed clay and peat at Allonby suggest this might have been a soggy area like the lagg fen that circumscribes a bog, where trees find it hard to grow; after the sea-level rose and the fen was inundated, the hollow trapped water-borne detritus; sometimes sand was deposited on top of the peat; a ray’s egg-case was caught in a crack and later buried. Later, when the peat and clay were higher and drier, fresh water seeped down through the peat and onto the clay, carrying red iron salts that accumulated in holes and hollows. And here at Allonby these colourful ferric salts accentuate another puzzle: tubes with hard, ochreous-red walls projecting upwards from the clay.

Tubes and burrows

Peat and clay are not dead and sterile environments – all manner of creatures, from invertebrates to single-celled bacteria and micro-algae – are adapted to make these substrata their homes.

Piddock holes in the peat

Piddocks are extraordinary: these bivalve molluscs (think of them as much fancier relatives of mussels) normally live, protected, inside rock below low-tide level. The animal’s shells are intricately patterned with sharp, toothed ridges and, by extending and retracting its muscular foot, and shoogling its file-like shells, the piddock gradually bores in, living within the burrow, enlarging the diameter – but not the entrance – as it grows, feeding on particulate matter in the sea-water. Burrowing would be laborious, unless the larval piddock finds and colonises a bank of peat that has been uncovered by the sea. Twice I have been excited to find peat that has been riddled with piddock burrows – one time the white shells of the long-dead animals were still trapped inside. That newly-revealed peat contains piddocks and their wide-diameter burrows, shows that this is not the first time it has been uncovered: it must have been exposed to the sea at a subtidal level for at least several years before it was buried again beneath the sand.

And what of the tubes in the clay at Beckfoot, found in January this year? Some were U-shaped, many were infiltrated with sand.

Mudshrimps dig U-shaped tubes of this approximate size; the tubes of mud-dwelling ragworms are more branched. Clay is much denser than the mud where these creatures normally live – but perhaps it was softer and muddier before it was compressed … It’s frustrating not knowing who constructed those shelters, and when.

And finally, to those strange reddish tubes jutting upwards from the Allonby clay: some of them are nearly a centimetre in diameter; their walls are hard, the material filling the cavity difficult to identify. Further along the exposure, though, are narrower tubes, and tubes in longitudinal section, some of them branching, many with traces of red pigment outlining the edges. What creatures constructed these?

But that is the wrong question, the wrong ‘Kingdom’ – the origin is plant not animal. In places filaments stretch between the broken ends of tubes and it’s clear that the burrowers were roots, and the walls of the tubes have formed around them, the clay hardening and taking up the ferric salts. Some are fine and fragile, others stout and thick-walled.

These tubes, then, are much more modern and unconnected with inundation by the sea. At the edge of the eroded face of the dunes, the mat of vegetation that stabilised the surface now teeters, and roots of the grasses and other plants dangle in the air.

Red clay

Having seen this new evidence of the Solway’s geological history, I went back to Beckfoot to see whether more sections of the submerged forest had been uncovered. But the small area of trees and peat that had been revealed in January had vanished – all that remained was the clay; peat and trees had been battered and swept away when the very high spring tides and strong winds had churned the sea into brown, froth-edged breakers.

However, the layer of red clay was still visible further to the North. It occurs at various places between Allonby and Beckfoot, and is coarser and more granular than the grey boulder clay. It would be possible to roll it into a ball, and press a stick through it to make a hole, smoothing the edges with your thumb. You could make a loom-stone or a fishing-weight, similar to those that I and others have found along the shore.

For more about the Solway’s geological past and the ‘dance’ between the land and sea, see The Fresh and the Salt. The Story of the Solway, published by Birlinn Books September 2020, and the related website.

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