The submerged forest

The forest, looking North to Silloth and the sea (Photo: Ann Lingard)

From the Mawbray Banks carpark just opposite the Bank Mill Nurseries and Visitor Centre, walk down the track to the dunes, and then along the short sandy path to the top of the beach. Stand there, on the pebbles, looking across the waters of the Firth towards the granite bulk of Criffel. If you are lucky, you may see low dark ‘cliffs’ on the shore, about 100 metres along your Criffel sight-line – a half-metre high, the patches of black are like shadows along the sharp edges of channels in the sand. Now 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 contains 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 forest at Mawbray, with Criffel across the Firth. (My grateful thanks to Joan Thirlaway for this photo.)

Now you see it, now you don't

However, the Solway’s tides and sands are capricious, and there will be many occasions when you go down to the shore and will find no sign at all of the ancient, submerged forest. One person I spoke to, who regularly surveys the Upper Solway’s shores, had never seen or even heard of the forest, and Brian Blake, whose excellent book The Solway Firth (published in 1955 and now, sadly, out of print) is illustrated by photographs taken by J. Allen Cash, notes that “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.”

The late Norman Hammond, who used to lead guided walks along the shore, once told me that, “The best time to see the forests will link in with extreme high water springs and a few days with a severe gale-force blow from the North-West or better still the North-East. The North-East severe gale will move the south shore sand away on a massive scale and reveal the forests - and usually a host of last war remains as well. It’s a case of dropping everything and getting down to the shore when conditions are okay.”

A tree-stump and roots  which appeared from beneath the sand in Spring 2011 (photo: John Lackie)

Well, it's always good to get down to the shore, even when conditions are not okay, and I have twice found the forest on Allonby Bay just South of the village, and once off North Lodge between Allonby and Dubmill Point. In the latter case, as at Beckfoot, there was no need to wait for the low Spring Tides – the forest was visible on the mid-shore, briefly exposed by the fierce northerly gales.

So how did a forest come to lie underneath the Firth? The obvious answer is “because the sea-level rose”, but of course the Solway has its own particular complicated version of events, which is explained beautifully simply at the  Solway Coast Discovery Centre at Silloth. The Centre is in the converted red sandstone school, and the offices of the Solway Coast Area of Outstanding Natural Beauty are at one end of the building in the former Headmaster’s House. Brian Irving, Manager of the Solway AONB, designed the exhibition and is almost evangelical in his enthusiasm for everything to do with the Solway. Our discussion ranges from topic to topic, with frequent interruptions to ferret through books, and to check the maps of the coast and the channels and the other nature reserves that are pinned to the walls. We also go through to the Centre to look at the models that Brian has commissioned to explain the protracted contest between the sea and the land.

Ice and sea

Brian explains that, during the last Ice Age, one huge glacier swept south and east to the Tyne from Scotland, meeting another glacier that ground its way North and West from the ‘Lake District’; as these melted, a large lake of glacial meltwater formed in the area bounded by the Scottish lowlands, the Pennines and the Fells. Then, as the ice retreated, so the shores of the lake were gradually colonised by plants and animals. What went on here was a reflection of everything else that was going on at that time in Britain, Brian tells me. “There was a wave of plant colonisation spreading North, a ‘tundra front’ moving North, with dwarf plants – dwarf willow and dwarf birch. It was the standard ecological colonisation.” Tundra vegetation: juniper, and low, flattened willow, dwarf birch, and blaeberry blazing red and orange in the autumn, clinging to the sparse soil that is only inches above the permafrost - try to imagine it spreading across the land from Silloth down to the Mersey and across to Galloway and Dumfries.

Then around 8000 years ago the air and soil started to grow warmer, and wind-blown tree seeds were able to survive and germinate. According to Brian, a pine forest gradually spread across our landscape, obliterating the tundra vegetation and lasting for a couple of thousand years. Mammoth, bison, giant deer and sabre-toothed cat grazed or hunted amongst the trees and on the grassland. Maybe the landscape looked like that around Victoria Bridge just South of Rannoch Moor, where remnants of ancient Caledonian pine forest still hang on. The forest there is sparse, the remaining trees scattered amongst the rocks and heather and pale tough grass, and beneath them you can see an older forest, its bleached trunks and branches exposed where the peat has been cut to make a deep ditch.

A sodden landscape: present-day Drumburgh Moss (photo: Ann Lingard)

The “Solway” pines, though, began to disappear about 7000 years ago, succeeded by deciduous trees like oak and alder and hazel. This new forest was low and dense with a thick understorey, Brian says: “You’d have found it almost impossible to walk through.” But perhaps you would not have wanted to, in any case, because this was a time when wild pigs were common. The forest would have been full of bird-song, you might have caught sight of elk or deer grazing, or even the now-extinct Auroch, Bos primigenus, a large ‘wild cow’.

We think of geological change in terms of blocks of time: 9000 years BP, 7000 years BP. But of course the process of change is gradual, and during this period the glaciers, here and elsewhere on Earth, were continuing to retreat and pour their melt-waters into the sea. The sea-level rose gradually and inexorably. It crept higher on the southern shore of the huge forested “Solway” basin, and the salt water oozed amongst the trees. Salt crystals blocked the water-channels within the tree-trunks so that the branches died of dehydration. “It was like beaver damage,” according to Brian Irving. “The twigs then the branches die and fall off, and you’re left with the spikes of stumps sticking up in the water.” Once the sea had made an entry it washed in further and invaded the immense freshwater lake, and so the Solway estuary was born and broadened, fed by rivers of glacial meltwater, and flushed twice daily by the tide. The forest was drowned beneath the Firth, and should have been destroyed and lost forever. In theory, we should not even know it had been there.

The glaciers were melting. Imagine those huge masses of ice and boulders, weighing down and compressing the land; as they retreat, the pressure on the underlying land is released and the land rises again, a slow process called isostatic rebound. This is what happened in the Solway basin, twice. The sea flooded in and drowned the land, but the land then rose; the still-rising sea encroached again but yet again the land rose. The evidence is there in the two “raised beaches” – the road from Allonby to Mawbray runs along the “Twenty-five Foot” or “Neanderthal” raised beach.

Peat and mire

But even this story is probably too simple. Frank Mawby, the former manager of English Nature (as it was then) told me, “There would have been little islands at high water, and some quite dramatic drops in sea-level too. If you look at the marshes today, you can see little bits of raised beach all over the place.” In some places growing trees would have been overwhelmed by peat rather than by the sea. A local geologist stressed the fluctuating climate and conditions: “There’d be a wet period when the woodland would retreat, then this would be followed by advantageous conditions for a couple of hundred years, so you get the trees re-invading. There was constant change.”

Peat and tree, 2014. (My grateful thanks to Joan Thirlaway for this photo.)

As for the drowned forest, each time the land rebounded some of the forest was lifted too. And with regard to that wet period, never complain that “it always rains in Cumbria”! About 7000 years ago, in the Atlantic Period of the Holocene, the climate was especially wet, the hills were almost permanently hidden in cloud and the rain poured down, day after day. Plants struggled to survive in the water-logged ground. These were perfect conditions for sphagnum moss to grow and accumulate water like a sponge. Reeds flourished but most of the other vegetation died and decayed and became compressed to form peat; the peat spread, blanketing the valley floors and creeping up the hillsides, burying the remains of the forest. On the raised beaches, the peaty “raised mires” formed. Hundreds of years passed, the mires or “Mosses” dried out, sedges grew, the moorland was colonised by woodland carr, silver birch and heather. The drowned forest was hidden deep down beneath the layers of peat and vegetation.

Bog-bodies?

Tree-trunk (photo: Ann Lingard)

Peat is cold, oxygen-depleted, acidic, a good preservative. It preserved the “bog bodies” of Lindow Man (Cheshire) and Tollund and Grauballe Man from Denmark. The skin of bog-bodies is tanned - a chemical process similar to turning hide into leather- and their internal organs and skeletal framework are often remarkably intact. (A surprising discovery was that Grauballe Man had undergone some posthumous cosmetic surgery: his chubby cheeks had been padded out with plasticine by the museum’s curators in the 1950s!).

Are there “bog bodies” buried in the Solway peats? Picken records evidence for finds in bogs on the Scottish side, but when I asked Frank Mawby if there were any “bog bodies” in the English Mosses, he laughed and said, “No. But there was a cow found in Solway Moss!” The "Solway Cow" is actually the remains of two adult cattle, whose hides, head and feet have been preserved. It is thought that they had been pushed into or suspended above a bog pool, and this had been "a product of human activity, rather than an accident", according to Dr Dave Wilkinson at Liverpool John Moores University. Unfortunately the Solway Cow wasn't accompanied by any "bog butter”, such as that described (p153) by Williams as coming from Lochar Moss, Dumfriesshire: "a white cheese-like solid ... which melts to a pale yellow liquid ...with a faint smell of rancid butter". (A 10-kilo lump of  bog-butter was found recently in an Irish bog, "[A] creamy white dairy product, which smells like a strong cheese and is believed to be about 2,000 years old.")

Tree-stump, 2014 (My grateful thanks to Joan Thirlaway for this photo.)

Typing the forest trees

Brian Irving told me that very little biological research has been carried out on the Solway's submerged forest. “The conditions were acidic so you wouldn’t get survival of calcareous shells, so there’s no evidence of land snails. Our information is based on things which survive the acidity – mainly plant remnants, pollen ...” Apparently an attempt was made about 25 years ago to radiocarbon-date a fragment of wood from the forest that lies just South of St Bees’, but I have been told there was some problem with the sampling technique; “8000 years old” is the date that’s quoted. Sampling of trees from submerged forests further South along the coast suggests dates of about 7500 BP.

I cannot pin down whether the submerged forest was oak or pine. One geologist thinks it was oak. Brian Irving thinks it was pine. Brian Blake writes in his book that “I was told that from some of the remains, and the prone trees are more than stumps, hazelnuts sometimes are found.” When I put the question to Frank Mawby, he said at once, “Oh – probably birch!” but then added, “I brought up a hazelnut once from seven metres of peat on Wedholme Flow.” And at Wedholme he found a layer of marine sediment overlying the peat, further evidence of that dance between the sea and the land. I’m surprised that opinion is so divided about the trees. Would there be any DNA remaining in preserved cells deep within the wood that would make the identification possible, or would it be too fragmented? After all, Tollund Man’s brain is apparently sufficiently well-preserved, after 2500 years, to allow extraction of genetic material.

Surprises at Beckfoot

Peat and clay (Photo: Ann Lingard)

It's a surprise to come across peat on a sandy shore - and in several places, you might also come across clay, perhaps inadvertently because the ground is suddenly alarmingly slippery underfoot. This blue-grey boulder clay or till is exposed where the peat has been eroded, and is further evidence of the Solway Basin's hot-and-cold past, as the clay was formed as the glaciers ground their way over underlying rock.

Piddocked peat (With thanks to Val Corbett for permission to use her photo)

And I had another surprise some years ago when I found a bank of peat that was riddled with tunnels, from which the white shells of long-dead piddocks protruded. This was strange and exciting, because piddocks are bivalve molluscs that normally burrow in rock. I keep hoping to find the piddocked peat again, but it must have been buried by the sand or broken up by the sea, for on one of our beach walks this year, someone found a remnant - a single piddock.

Useful information

The Solway Coast Discovery Centre is at Liddell Street, Silloth-on-Solway, CA7 4DD. Telephone 016973 33055 for further information or go the Solway Coast AONB website

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