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Landscape Mysteries Field Trip

Updated Wednesday, 13th July 2005

Anne Burgess reports on the OU Geological Society visit to the Shetland Broch towers in 2004

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A broch

Over a year ago OUGS President Chris Wilson circulated to Branch Organisers brief details of the then forthcoming Landscape Mysteries BBC television series to be presented by Professor Aubrey Manning and screened in autumn 2003. He invited Branches to arrange field trips to complement the series.

The East of Scotland Branch decided to base such a trip in Shetland, which was featured in programme four, titled The Tower People of Shetland. Shetland has some spectacular geology, with everything from ancient metamorphics to fossiliferous sandstones, and having enjoyed a previous Branch field trip there we knew that all the necessary expertise was on hand in the shape of Shetlander Allen Fraser, a long-standing OUGS member, and Deborah Lamb, also resident in the islands and researching for her PhD in archaeology. The Shetland Field Studies Group also offered enthusiastic support.

We thought it unlikely that there would be much custom for a day trip at the time of the broadcasts in 2003, because many people perceive Shetland as being far away, and the days there are too short in autumn and winter to see enough localities before it gets dark. Besides this, we wanted to visit Mousa, which is not possible in autumn or winter because the ferry does not operate. So we decided on a long weekend the following July, to give people plenty of time to make up their minds to join us. In the event this proved a wise decision because the BBC delayed transmission of the series for about a month.

In response to suggestions from members of both the East of Scotland and West of Scotland Branches we added two extra pure geology trips before the main event, and sent out the details to those who had enquired. After a few anxious weeks, when we began to wonder if the trip would be viable, bookings started to pick up as spring approached, and eventually 27 people travelled to Shetland for the occasion, while 17 members of the Field Studies Group joined the party for one of more days.

The first trip was to see the volcanic area of Esha Ness. The cliffs show many fine examples of airfall deposits, tuffs and agglomerates, as well as lava flows - in one place we were able to count eight separate flows - of andesites, mugearites and rhyolites, often with flow banding. We walked north in brilliant sunshine to the Grind of the Navir, a cleft in the cliffs, which at this point are formed of a classic ignimbrite. The power of the sea is evident from the storm beach of slabs up to 2 metres long thrown up to the top of the 30-metre high cliffs and then 100 metres inland. Returning by the Hols o' Scraada, where a cave collapse has left a chasm linked to the open sea by a 100-metre subterranean passage, we noted our first broch, then continued to Braewick, where we examined some curious striped sandstones, and argued at length about their formation.

Next day we traversed the largest island, Mainland, from west to east, to examine Moine and Dalradian metamorphic rocks. First we stopped at the Scord of Sound viewpoint from which the effects of the underlying geology on the landscape can easily be seen. Then into Ward of Tumblin Quarry, which features an unusual foliated monzonite of the Aith-Spiggie intrusive complex. In the Burn of Lunklet we examined deformed high-grade metamorphic rocks of the Boundary Zone; despite animated discussion and imminent risk of various people falling in, we could reach no consensus on the formation of a very curious feature in the stream bed. A walk down to the shore at nearby Burra Firth took us to some spectacular ptygmatic folding, and up at Hill of Lee we examined microcline megacrystals in the Valayre Gneiss outcrop. Near Aith we stopped to look at the Weisdale "Limestone" (actually a calcite marble) and boudinage in psammite by the burn. Next we clambered down to the shore by the Whalsay ferry terminal at Laxo to see complicated folding and interbanding of calc-silicate and semipelitic granulite, and red granodiorite of the Graven Igneous Complex with typical hornblende xenoliths. The final port of call was the huge exposure of Valayre Gneiss in Grutwick Quarry, whence at least one large block made its way south as a souvenir.

After a free day, during which we anxiously watched while swirling fog threatened to prevent the rest of the party's arrival in Shetland, everyone finally arrived in time for the weekend's events, though not everyone made it in time for the excellent talk by David Jackson on archaeological artefacts, which set the scene for the next few days.

First stop on Friday was Garths Ness, close to where the 'Braer' went aground in 1993. In the schists at this locality is a massive zone of sulphide mineralisation which was exploited for copper in the early 1800s, but proved uneconomic. However it may also have been worked in the Iron Age. Still on the theme of copper, we next visited the site of the Sandlodge copper mine at Sandwick, where 12,000 tons of copper ore and haematite was extracted intermittently between the late 18th and early 20th centuries. Some idea of its scale can be gained from the width of the main lode, which is 9 or 10 feet, and the extent of the shafts , of which the deepest cut the lode at 240 feet. After lunch the party embarked on the Mousa ferry to visit the famous broch, the best-preserved of the numerous ones in Shetland, Orkney and northern Scotland. We were able to examine all the features typical of brochs, to climb the original stairs between the double walls, to appreciate the site and the view from the roof, and to consider the mystery of why the brochs were built, and how they were used. Our last stop of the day was Burland Croft, where Tom and Maggie Isbister are farming in the traditional way. We encountered a bewildering variety of Shetland livestock breeds from ponies to tiny chicks, sampled Maggie's scones baked with bere (an ancient form of barley), enjoyed traditional tunes on Tom's fiddle, and admired the elegant lines of the clinker-built boat he had almost finished working on.

Saturday dawned wet and windy, but we set off, undeterred, to take the two ferry crossings to Unst, the northernmost inhabited island in the United Kingdom. Unst is also largely composed of an ophiolite whose characteristic features have shaped the economic use of the land. At Underhoull, while the broch is not nearly as well preserved, it is surrounded by a complex of earlier and later buildings, notably a souterrain and a Norse farmstead. Despite the rain, we were able to visualise something of what life might have been like for the broch builders and their successors. We went on to Clibberwick, where the serpentine of the ophiolite has become altered and is worked for talc; beyond the quarry we slithered down to the beach of black serpentinite cobbles and white talc outcrops. We were glad to be able to stop in the nearby shop and self-service cafe for lunch under cover and a brief visit to the Unst Boat Museum. Then it was off to Hagdale to the chromite mill; this was a major disappointment to those of us who had been there four years earlier, because the mill had been neglected and was overgrown with grass and weeds. We did our best to clear the worst of the growth so that the features could again be seen. Our plan had been to walk up to the chromite workings, but the rain had washed away all enthusiasm, so we repaired instead to the Heritage Centre to visit at second hand instead.

Although still grey on Sunday, it was at least fair, and we headed west to Scord of Brouster, where the remains of Neolithic houses show that it was farmed for over 3000 years. Just as the record of climate change can be seen in sediments, it can be traced in the changes in settlement of marginal land – occupied when the climate was benign, and finally abandoned as peat spread over the former fields. The Broch of Cuslwick was our next port of call, involving a change of coach and a two-mile walk to the site, which, like all broch sites, is well-chosen for defence atop a cliff and with a loch on the landward side and surrounded by former farmland. It is built of massive blocks of the local pink granite, and many typical broch features can still be seen. Further along the cliffs we viewed what is thought to have been a monastic settlement perched on a pair of almost inaccessible offshore rock stacks, and on the way back we inspected one of the enigmatic ‘burnt mounds’ which are so numerous in Shetland. After a brief stop at a roadside quarry to collect samples from the Sandsting Complex, our last stop was the impressive Bronze Age Staneydale ‘Temple’, a large building with massive walls whose purpose is unknown, but has similarities to temples found in Malta and Gozo. It stands in one of the few places in Shetland from which the sea cannot be seen. On the way home we observed the Law Ting Holm, the ‘parliament’ of Norse Shetland, and several more features of the ‘Bronze Age’ landscape in the Tingwall valley.

Our final day’s trip took us first to Old Scatness, where teams from the University of Bradford are excavating a bewildering complex of Iron Age buildings, and to apply modern archaeological methods including radio-carbon dating to the excavations. These have revealed that the Scatness Broch, at least date from 400-200 BC, and it is surrounded by wheelhouses and evidence of later occupation. On the site are demonstrations of ancient toolmaking, brewing and other crafts, with a chance for visitors to try their hand with some of the tools. Sadly much of the site was literally ‘under wraps’ but there was enough on view to impress us all with the sheer scale of the site. Not far away is Jarlshof, where excavations in the early 20th century revealed a record of occupation for some 5000 years, from the Neolithic until the 17th century, including a Bronze Age village, another broch, wheelhouses, Norse longhouses, a mediaeval farm and finally the Old House of Sumburgh. A team is currently excavating here too, and we were shown the various pits and the additional features they are revealing. After lunch at Bigton, by the elegant tombolo which links St Ninian’s Isle to Mainland, we made for Catpund. On the way up the track we admired an outcrop of komatiite lave, which is extremely rare in rocks as young as the early Ordovician, and bands of serpentinite; our objective was the steatite outcrop quarried 4000 years ago for material to strengthen pottery, and later used by the Norse for raw material which they carved into bowls and utensils. The outlines of the carvings are still clearly visible in the soft rock.

This was our last port of call, and we made our way back to Lerwick where many of the party were due to depart on the Aberdeen ferry, and waved them off on their journey.

Over the week we all gained a great insight into the geological and human history of Shetland, and in particular the way the geology governed the land use and way of life of the early inhabitants, and the effects of climate change on settlement patterns and agriculture – and hence on the landscape as we see it today. But the mystery of the brochs remains.

 

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