Darwin’s Lochaber Lesson
The Parallel Roads of Glen Roy are an enigmatic feature that generated great controversy during the 19th century. The mysterious parallel lines that are traced along the sides of Glen Gloy, Glen Roy and Glen Spean became internationally famous .
The features, best seen on the sides of Glen Roy, were the subject of the most substantial piece of fieldwork that Charles Darwin undertook upon returning from his voyage on the Beagle, at a time when he was establishing himself as a geologist.
Darwin theorised that they were raised beaches, or shorelines made by the sea, and that the landmass then bulged up raising these beaches to their present height. However Louis Agassiz proposed an alternative explanation of the “Roads”, in terms of vanished glaciers, which is the theory we still accept today.
There have been many theories for the lines, from ‘hunting roads’ for the Celtic Warrior Fionn mac Cumhaill to one road for travelling up the glen, another for coming down and another for driving cattle! However by the early 1800s the “Roads” began to attract serious scientific study although there were different ideas as to whether they were formed by human action or they were shorelines of some lost loch. In particular Thomas Telford, the famous Scottish canal and road builder thought that they had been constructed by human endeavour, presumably whilst he was working on the nearby Caledonian Canal. However the theory that they had been created by water became accepted as being the most likely. The problem was, how had the water been able to create the shore lines?
Darwin was sure that sea levels had fluctuated and was convinced that he would discover marine shell remains, but despite much searching he failed to find any. However he still produced a paper, that as a recently accepted member, he presented to the Royal Society in1839. Darwin agonised over his theory before eventually admitting his ‘great blunder’ and accepting Agassiz’s theory.
In 1840 Louis Agassiz made a visit to London and Glasgow and subsequently to the Highlands where he examined evidence of glaciation. Although many geologist were aware of a theory of ice covering much of the world, this was previously unknown and almost incomprehensible to the British public at the time.
Upon examining Glen Roy, Agassiz proposed that there had been a glacier in Glen Roy cutting off the normal drainage system. The water which had normally flowed out of the Glen became trapped by a glacier that pushed up into the mouth of the glen. The watered pooled, forming a lake which would have filled until it reached a level at which it could escape.
The Stand Off
Darwin stubbornly refused to accept the new ‘ice’ theory for twenty years. During this period various well-known geologists visited Glen Roy and refined Agassiz theory. In 1861 Jamieson used new theories on glaciation, the idea that the ice flowed as a viscous fluid, and together with evidence of a previously unnoticed col at the height of the second ‘road’ wrote the whole story which is still accepted today. He could now explain the movement of glaciers which would have advanced into the glen, cutting off lower locations where the water could escape, forcing the lake level to rise to the next available col over which it could escape. For the intervening period whilst the glacier moved slowly forwards the water level would remain static and that wave action would have, over time, cut a recess or shoreline. A similar process would have occurred in reverse as the glacier retreated reinforcing the shorelines.
In 1863 Darwin finally accepted that it must have been glaciation which created the “parallel roads”. However, by that time he was deep into the controversy about the origin of species, his most famous scientific legacy.
A Note on Darwin
Finally it is interesting to note Darwin’s great disappointment and how it reflects on his humanity. His theory was plausible considering his recent voyage and the evidence he had acquired in South America of raised beaches. It was in reality no real blunder but different ideas from a separate field of study that made the difference. However it does make Darwin a much more human figure who strode about the hills of Glen Roy and enjoyed the gorgeous sunsets and nature, looking as happy as he felt whilst being so interested in this remarkable area. Something to bear in mind when you visit!