The Parallel Roads of Glen Roy

They were a mystery that baffled scientists and legend makers alike; a conundrum with a thousand answers, each as wonderful and often ludicrous as the other – and for hundreds of years the Parallel Roads of Glen Roy provided a ready source for the kind of folk tales enjoyed by Highlanders. The solving of the puzzle would however reveal a story far more fantastical and unimaginable than any fairy tale could conjure; and gives us an insight to the incredible story of Scotland, and the world.

Glen Roy is a narrow, steep-sided valley branching off from the wider Glen Spean about 15 miles north of Fort William and the high peaks of the Ben Nevis Range. Glen Spean in turn opens into the broad, straight and imposing Glen Mòr, or Great Glen. This geographical arrangement would have a significant bearing on the story. Curiously, Glen Roy has a ring of terraces or ‘roads’ running the entire length of the valley on one side which is then mirrored at the exact same altitude on the other. They look man-made, but are so precise in keeping their height and remain parallel to each other that some other-worldly influence seems present in the formation. There are three distinct terraces ringing the valley, one at 850ft, the next at 1066ft and the highest at 1150ft above sea-level. This uniformity and curious nature of their existence in this one valley spawned countless myths and stories.

Legend had it, they were built by the Romans to race their chariots; or perhaps by our Pictish ancestors as a running track to prove one’s manliness. Others suggested they were constructed by the legendary Fionn MacCuimhaill as an aid to hunting some mysterious beast in the mountains of Lochaber. The fairies built them as part of their ancient magic, or the Gods for us to worship; and, religion would be a major player when the real investigation started.

The Scottish Highlands are littered with large mounds; boulders in the wrong places, knows as erratics; and high terraces lining many of the straths and glens. There didn’t seem to be any natural reason or cause for this, or indeed why the landscape should be the shape it is. Until the middle of the 19th century the only plausible explanation was Noah’s Flood – and that these phenomena were thus created by the receding waters; and, this simplistic biblical mindset was stubbornly resistant. However, in-roads and alternatives were being espoused. Scottish geologists James Hutton and Charles Lyell had begun to explain the processes of how the earth was formed over huge eons of time, and that these processes are on-going. This was of course a direct challenge to the 7 Day Creation story, and it took a lot of persuading for it to become mainstream.

Thus, they said, geological action over vast periods of time, and weathering could account for many of the features found in the Highlands; but, the Parallel Roads of Glen Roy had them stumped. These were clearly not river terraces, nor laid down in geological sequence. Lyell, and even Charles Darwin looked to explain the mystery. In the 1830s both men became convinced that what they were looking at were ancient coastlines, beaches formed when the sea was much higher (or the land much lower) than today. This kind of correlated with the Flood proposal, and many stuck to the older theory. They would all be proved wrong; and when the answer finally came, it would revolutionise the story of the planet, and rock the scientific world to its core.

During the 1830s the revolutionary Swiss geologist Louis Agassiz proposed that his Alpine homeland had once been covered by a massive ice sheet similar to that of Greenland, rather than the network of sinuous glaciers snaking down from peaks as now. This had been brought about by detailed work examining rocks, terraces and deposits; and, in 1837 he published the idea that the world had once been subject to an enhanced glacial episode. So, armed with the know-how he came to Scotland in 1840. Here, where no glaciers existed, Agassiz and his colleague William Buckland showed substantial and evidential proof that the mountains and glens had been in the past subjected to intense glaciation – the same mounds, deposits, scratches (known as striations) and erratics found in the Alps were all over the Highland landscape. It was empirical confirmation that Scotland too had once been under the action of an ice sheet and multiple glaciers. But, what of Glen Roy and those pesky roads?

In a moment of clarity, Agassiz, who dedicated much of his research in this area concluded that the terraces were shorelines formed by fresh-water lakes dammed by ice in the main valley. In 1863 Thomas Jamieson published a paper on the ice-age origins of the parallel roads: his conclusions settled the debate once and for all.

Towards the end of the last Ice Age, around 11,000 years ago, ice once again thickened and spread to fill the wide basin of the Great Glen in Lochaber; which as it grew spilled into Glen Spean. This then blocked off the potential for meltwater in Glen Roy (and also in Glen Gloy) to escape to the sea. So, what are known as ‘ice-dammed lakes’ formed, leaving the tell-tale shorelines. As the ice continued to thicken, the lake level rose: marked out by the three terraces. Eventually, the water level reached the point where it exceeded the altitude of the watershed at the head of the glen, and over-spilled into the River Spey catchment and flowed to the North Sea.

Around 10,000 years ago the climate warmed dramatically and the ice melted quickly away; and, with the blockage gone the lake could drain down into the Atlantic – it may have been quite an explosive event, and the valley all the way to Fort William is littered with gravels from the disgorging of the lake. Understanding the processes involved in the formation of the parallel roads completely re-wrote our understanding of the earth’s glacial past; revolutionised the study of ancient landform creation (evidence of enormous ice-dammed lakes would be found in North America for example); and, without the mystery of the Parallel Roads of Glen Roy those discoveries may have been decades in the finding. Figuring out this enduring mystery was the Eureka moment in the study of the world’s landscape history; and aught not to be forgotten.

This blog was written by David McNicoll, owner of Highland Experience USA; who specialise in Scottish Travel Packages. Tours to explore Scotland’s incredible geography and scenery can be arranged.

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