How Scotland met England
The stones form an irregular circle, surrounding the taller stone in the centre. On one side of the small hill, an arm from the Atlantic ocean approaches, across a single-lane track. On the other side, a field, a small road and a few houses. Silence reigns: the only sounds come from softly-talking tourists, the nearby houses, the distant sea and the wind. A dozen or so hardy tourists wander around the stones. What each sees depends on how they look. Some take pictures on their phone, performing a modern ritual within the stone circle and its strangely off-centre burial mount. Others look in their mind and pay tribute to the lives of the ancient builders of 5000 year ago. But mist and rain are coming in and the people are leaving. One lingers to take a close look at the stones, before hurrying back to the semi-circular visitor centre. The stone circle is made from some of the oldest rock in the British Isles: the wet-grey surface reflects the deep mist of time. The silent stones have a story to tell.
The standing stones of Calanais (or Calanish) on the Isle of Lewis are an arresting sight. Who put them here and why? The location is, ignoring its modern isolation, well chosen, a ridge at the end of a 10-km-long, northwest-facing but sheltered arm from the sea. The ridge gives a view of the horizon in all directions: an ideal place to see the settings and risings of the Sun and Moon. On the horizon, the low hills resemble a female figure, called the Old Woman of the Moors (Cailleach na Mòintich); sometimes the moon appears to rise from her body, but whether that had any relation to the monument is hard to tell. I have some doubt: the frequent cloud cover means that only regular events were worth looking for, mainly the solstices and equinoxes. The central stone is 5 meter tall; the 13 stones encircling it are smaller. 40 further standing stones are at various distances, leading up to the main monument, Nearby is grassland with a few houses. Beyond the houses the gras gives way to boggy peat and small lochs. There are more stone age monuments in the area, though none as impactful as Calanais. They have been dated to about 2500 BC. Someone later added a burial chamber to Calanais, presumably when its use was already in decline. Its off-centre position detracts from the simplicity of the original structure. Sometime after 800 BC the site was abandoned.
Calanais is one of many stone-age monuments on the Hebrides, a series of some 500 islands off the Scottish west coast. Only some of the larger islands are inhabited. The inner Hebrides are closest to the main land, and the Outer Hebrides, also called the Western Isles, are further out. The largest of the Hebridian islands, surprisingly, has no unique name, in spite of being the third largest of the British Isles (the second largest is Ireland). The northern part is called the Isle of Lewis, and the southern (more mountainous) part the Isle of Harris, but there is no name for the whole, other than ‘Lewis & Harris’.
The Isle of Lewis (or half-island) waivers between beauty and bleakness. The Outer Hebrides face into the Atlantic Ocean with all the storms and rains it brings. Erosion has stripped back the land to an ancient bedrock, on which rain and a climate mildened by the Gulf stream has encouraged gras and moss to grow. The weather can be wild. (The word ‘Lewis’ comes from ‘leog’ meaning surface water.) The east side of the island is milder, sheltered from the force of the ocean; here the Vikings had their preferred harbour. But they were not the first ones to come here, not by far. People had lived here for at least eight thousand years already.
The main town on Lewis is Stornoway, the old Viking harbour, with some 8000 people. Fishing remains important here. The small-scale farming is called crofting, and the farmhouses are called crofts. Tourists come for the isolation, the monuments, and some of the best (and quietest) beaches in the world.
But the presence of people is comparatively recent. During the ice age, this area was deep arctic and completely uninhabitable. A small ice cap was even centred on Lewis, 400 meter thick and extending to near St Kilda. After the ice age, as Europe recovered people began traveling up the coast, settling on the Isle of Man, the west coast of Scotland and on the Hebrides. That was by 7000 BC. These first people lived through times of rapid change. The sea had been 50 meter below current level, leaving the isles connected to the main land. But when the ice melted, the sea rose rapidly. The people followed a shifting coast as the sea kept rising and land became island. Genetic evidence shows that people first spread from a Basque refugia (an ice age holdout), following a coast line which at the time connected to Cornwall and Ireland, and up the Irish west coast to Scotland. Other groups traveled from Eastern Europe, along the major rivers. In the early neolithic, there was a very similar culture along the entire Atlantic seaboard. Stonehenge and Calanais were build by cultural relatives.
The first people to come were coastal hunter gatherers. The sea provided them with food, but so did the land with nuts, berries and perhaps deer. Swans and geese may have been part of their winter diet. Farming supplemented the diet, perhaps brought in by the new arrivals from the east, and this became more important as the neolithic began and the nomads became more and more sedentary.
The land had thus been occupied for thousands of years before Calanais was build. A smaller structure had existed within the region now occupied by the famous stone circle since perhaps 3000 BC. 500 years later, the circle and accompanying stone avenues were brought to completion. Calanais stayed in use for the next 1700 years, but the usage changed with the culture. At some time the central burial mount was added. By that time it appears to have lost its original meaning. And finally, after 2200 year of use Calanais was abandoned. Soon it became covered under the developing layer of peat. By 1800 AD, the blanket peat had grown to 1.5 meter in thickness and covered much of the stone. In 1857 the monument was dug out and the full structure revealed to the modern world.
Why did people choose to live here, in such an unforgiving climate, and why did they leave? And how could they build such monumental sites in such a marginal environment? People living on the edge don’t have the resources to spend on large building projects. Calanais is often compared to Stonehenge, and although it is not at the same level of effort (and the stone was all harvested locally, unlike Stonehenge), it does represent a very large effort. Only a flourishing community could have done this.
The secret to this thriving community lies in the weather. So soon after the ice age, you might expect a chilly climate, still recovering from the extreme cold. But this was not the case.
7000 BC, when people first settled here, was in fact a remarkably warm period. The temperatures had risen very fast after the last stirring of the ice age (the Younger Dryas), to levels higher than those of the mid-20th century. Not only was the climate in the Outer Hebrides warmer, it was also less wet. The climate allowed forests to become established throughout the Hebrides. The hunter gatherers lived in a very different environment from what it looks like nowadays, with extensive birch and hazel forests even on the west side of Lewis, and oak trees in the sheltered east. Times were favourable.
But the good times did not last. The climate started to cool, and by 2000 BC, had become 0.5C cooler than before. That sounds like a small change, but is not. It had a dramatic effect on the forest. By 6000 BC, the forest first began to contract, and by 2500 BC the island had become treeless. The land became not only cooler, but also much wetter, with more rain and less evaporation. The drip-feed of the rain killed the trees and caused blanket peat to grow. The grass land became moor a boggy, water-logged moss growing deeper by an average of 10 cm per century. Neolithic farming, whilst increasing the available food supply, was dependent on weather and soil. After a few centuries, agriculture could not continue in the deepening bogs. Life became more difficult, and the resources needed to maintain and use Calanais were no longer there. I imagine the last druid knowing the rituals of the stones waking up one morning to find his only apprentice gone. Finally, the last people moved away, to more hospitable areas further east, abandoning the stone monuments to a memory of better days. 0.5C was all it took to end a way of life.
The reasons for the climate changes (which were global) are well understood, both for the warm period immediately after the ice age and the cooling which followed. They are related to changes in the Earth’s orbit. The cooling continued into the Little Ice Age (which really wasn’t so little, lasting 500 year). Only during the 20th century did the climate improve again, also for well understood reasons but now caused by human activity. The global warming quickly pushed temperatures back to where they had been during the Holocene optimum. But over the past two decades we have gone well beyond this and have entered uncharted territory. A change by 0.5C was the difference between a flourishing and a marginal community. We have no idea what a 2C change will do. More than that doesn’t bear thinking about: like the people who abandoned Calanais, many would become climate refugees, needing another place to live.
The people of Calanais, and the Lewisian communities that followed, lived through momentous changes. Even over their brief centuries, the Earth changed and the change affected the way they lived. But for the silent, stationary stones, these changes were just the last part of a far longer journey. Their story goes back more than half the age of the Earth.
The stones which form the Calanais monument are truly monumental. They are Lewisian gneiss (the name giving a hint to the location), which is the oldest rock in the British Isles. Gneiss is a metamorphic rock: it has been subject to extreme heat and pressure, enough to partially melt and re-crystalize it. The original structure of the rock is destroyed and it becomes a mesh, with large crystals, but it retains the original composition. Gneiss can be made from a sedimentary rock (such as shale) or from an igneous rock (granite). The heat transformation is more important than the original raw material. The final product depends on the source material, the heat and the pressure.
If there is high pressure but not much heat, rocks survive but are pushed out of shape. Fossils that have gone through this process come out recognizable but much more elongated than they were in real life, sometimes giving rise to hilarious reconstructions. Pebbles can become elongated, as in the picture below.
At higher temperatures, the rock changes character. Shale turns into slate. Turn the heat up further, and the slate becomes phylite, schist and finally gneiss, in a sequence from a layered to a granular structure. Start instead with limestone, and you get marble. (geology.com is a good source of information on these rock types.) As the rock metamorphoses, any pebbles fall apart and become crystals embedded in the mesh.
The formation of the Lewisian gneiss started 3 billion year ago. It began with an igneous intrusion, i.e. with magma that solidified underground to form granite. This granite became the main source material. Different regions in Scotland’s northwest give slightly different dates for the original intrusions, ranging from 2.6 to 3.0 billion year: it is possible that northwest Scotland was not a single region initially, but was assembled from different crustal blocks with different histories. The composition of the Lewisian rock suggests that a small fraction of the intrusion came from melted ocean floor and the rest from hydrated mantle material. The combination of the two suggests that at the time this was a shallow-angle subduction zone.
The metamorphosis into gneiss happened 2.48 billion year ago, in an event called the Badcallian. The structure of the gneiss and the pressure this required shows that it formed some 50 km underground, at a temperature of about 1000C. The depth exceeds the typical thickness of continental crust. Thickening crust and metamorphosis is a characteristic of mountain ranges, which is a good indication of a plate collision. The long time between the intrusion and the metamorphosis, up to 400 million year, shows that the mountain range was not caused by the original subduction zone, and was related to a different continental collision. This long ago, the continents may have been much smaller than they are now: the collision and its mountains may have been less like the Himalayas and more like the Alps although we don’t know this for sure. This far back, it is hard to know what collided with what.
The Lewisian rocks are cut by a number of dykes, called the Scouri dykes. These formed about 2.4 billion year ago, while the rock was at a depth of 10-20 km. The Scouri dykes are a famous example of how younger rock (‘younger’ in a relative way only – it is still ancient) can become embedded inside older material. It is quite probable that their formation coincided with volcanism on the surface, but that surface is lost to us. The Scouri dykes are more prevalent on the Scottish main land than on Lewis. There may have been a second phase of dyke formation around 2 billion year ago. A bit later still, new magma was injected and granite formed, and a second phase of metamorphosis began. This is called the Laxfordian; it happened 1.74 billion year ago, although different regions may have had slightly different dates. There are indications that at this time there was accretion, volcanics, and shear motion. Lewis thus was resembling California in its geology. The Laxfordian gneisses date from this phase: they formed at a temperature of 600 C and a depth of 25 kilometer.
Around 2 billion year ago, Lewis was embedded in a vast area which included the north of Scotland, the Baltic craton, Greenland and the Canadian shield, and possibly the North China craton as well. When this first came together is not well known, but the similarity of the rocks in these places is striking, and other places in these cratons show events around the same time as the Laxfordian.
The Lewisian rock didn’t remain underground. Over time, erosion removed the crust above it and exposed the deep layers. The volcanoes which probably formed on the surface especially in Harris were gone, leaving no trace. As the years came and went, at times the land was uplifted, and at other times it fell below the sea. New sediments were deposited on top, a thick layer of sandstone, but although this layer survives in places on the main land, on Lewis it too has been eroded away. The Lewisian rock lived through the building of mountains, as continents collided, and through the break-ups which saw these mountains divided over different continents; it saw the volcanic events accompanying both. Oceans came and went; continents drifted, merged, and separated. The Grenville rocks, which lie below Central Park in Manhattan, and come to the surface near the Lawrence river and west of the Appalachians, formed near here, during the closure of a long-gone ocean, 1.1 billion year ago; worn-down remnants that once were the Himalayas of their time, now reduced to piles of rubble.
The collision that caused the Grenvillian Himalayas was part of the formation of the Rodinia supercontinent. Lewis was in the middle of Rodinia; the sandstone sediment which covers the Lewisian rocks in many places (but not in Lewis) comes from the sand dunes in its desert interior. Rodinia survived for 300 million year, but eventually it broke up. One of the breaks occured 600 million year ago near the line of the Grenville mountains. Once more a new ocean formed. This ocean we know better, and we even have given it a name, Iapetus. Lewis found itself on the western shore of Iapetus, together with the northern part of Scotland and part of Ireland, and Canada. The platelet with Southern Scotland, England and the rest of Ireland was still far away, part of the opposite, eastern side of the ocean. A subduction zone formed on this eastern side, with volcanoes and island arcs, but the western side where Lewis was seems to have been quieter. When the Iapetus finally closed, the parts came together. Scotland emigrated across the sea to the eurasian plate, obtained asylum, (or perhaps the other way around) and the British Isles formed. There is still a notable stitch along the Scottish lowlands, from Edinburgh to Glasgow. The collision which closed the Iapetus formed the Caledonian/Appalachian mountains, ranging from what is now Norway to the southeast US. This was part of the formation of the most recent supercontinent, Pangea.
But continents are as temporary as the oceans. Pangea broke apart, and 60 million year ago the Atlantic ocean appeared. (In mythology, Atlas was the son of Iapetus.) The break-up was accompanied by vigorous volcanism, the remnants of which are still visible on Skye, the Cave of Fingal, and of course the world famous Giants Causeway. This time, the Isle of Lewis ended up on the opposite time to the previous cycle, on the eastern shore. Mammals had by now replaced the dinosaurs of Pangea and the world was finally becoming recognizable. The rock that had formed 50 km deep had again re-surfaced. The ice ages caused more erosion, by the scraping of the thick moving glaciers, but this too passed. And finally, people came and hewed at the stone to build Calanais. It must have been back-breaking work: the gneiss is incredibly hard, as it had to be to survive for 3 billion year. The migrant humanity build their monuments out of rock that had traveled far, wide and deep, two refugees thrown together at the rim of the world.
The changing Earth
The Earth we see today is not stable. People who study volcanoes are more aware of this than most: volcanoes do not live long, often less than 100,000 year, change their appearance and behaviour, and go dormant and extinct. New ones appear, sometimes following the drift of the continents. There have been many changes on Lewis in the 5000 year since Calanais was build. The sea shore has moved, the climate changed, and where there once was forest now there is moor. It is a different world.
But we are not good at noticing slow change. We hanker back to a past that in our mind was a little different but a lot better. Our rose-tinted memory cannot comprehend or even recognize much of the change, and it forgets much of the past. The slow change of the Earth goes us by, until the problem of Calanais brings home the reality of change, and the change of reality.
So much has changed: the landscape, the climate, the people. The people who made Calanais could not have envisaged the place it is today, and would not have recognized the land. If 5000 year does that, how different was the world ten thousand, a million, or a billion year ago? Touching the stones (which, unlike at Stonehenge, you can still do), you feel a rock that formed when the world was young. What was this world like? The stones can’t say – they do not speak. If they could, they would tell us of a world with unbreathable air, a barren land and a sea with only a few algae. But the forces that shaped the Earth were already there. Continents drifted and collided; ocean crust formed and subducted; volcanoes build mountains and erosion took them away. Rivers carried the sediment back to the sea from where it had once come. By the time the rock reached the surface, after 50 km of crust had eroded away, the Earth had changed. The atmosphere had improved but still wasn’t breathable, at least to us. Life, rare 3 billion year ago, had grown in abundance and complexity but hadn’t yet left the sea. The continents had grown. But it was not yet the Earth we know today. That came much, much later.
The stones of Calanais make you think. All the changes that have happened since it was build are a blink of the eye to the Earth. The stones remember far older times and have lived through far larger changes. To them, the Atlantic ocean formed yesterday. Events 2 or 3 billion year ago left their mark on the Lewisian gneiss. It remembers previous oceans, and the formation of mountains long gone. It saw England first attached itself to Scotland. The stones deserve to be noticed. Calanais is a tribute to the history of the Earth.
VC now celebrates its fifth anniversary. It too has lived through changes and upheaval, slow changes and big eruptions, and has lived within a flourishing community. VC aims to help the readers and contributors to understand a little more of the Earth we live on. Like Calanais, it makes us think. Cheers!
/Albert Zijlstra, November 2016