Glen Roy in the Lochaber area of the Highlands of Scotland is a National Nature Reserve and is noted for the geological puzzle of the three roads ("Parallel Roads"), which are in fact preserved ice-dammed lake shorelines, from a brief (some 900-1,100 years in duration), climatic deterioration, during a much longer period of deglaciation, subsequent to the last main ice age (The Devensian). From a distance they resemble man-made roads running along the side of the Glen, hence the name. The glen runs north from Glen Spean which takes the main A86 trunk road and the railway of the West Highland Line, both running about a further 14 miles southwest to Fort William. Roy Bridge railway station and the village of Roybridge are sited where the River Roy joins the River Spean, and from there a narrow single track road runs north up the glen for almost 10 miles to Brae Roy Lodge.The Parallel Roads of Glen Roy, Scottish Highlands, represent a series of ice-dammed lake shorelines produced during the cold climate of the Younger Dryas (GS1). It has been demonstarted by Dawson, Hampton, Harrison, Greengrass and Fretwell (2002) that each lake shoreline exhibits evidence of glacio-isostatic tilting associated with the decay of the last (Late Devensian) ice sheet. The directions of tilting of the three shorelines (in the quadrant between north and east), are at variance with published glacio-isostatic uplift isobases based on marine shoreline data that suggest a pattern of decreased uplift towards the northwest. The gradient of shoreline tilting (between 0.11 and 0.14 m km-1) is similar to measured regional tilts of a well-developed marine shoreline (the Main Rock Platform) considered to have been produced in Scotland during the same period of extreme cold climate. Consideration of the ice-dammed lake shoreline data also points to the former occurrence of two separate episodes of tectonic activity during the Younger Dryas (Greenland Stadial 1 - GS1). In the 19th century, the Parallel Roads attracted the attention of many of the founding fathers of modern geology, including the Reverend William Buckland, James Geikie, Charles Darwin, Charles Lyell and Joseph Prestwich. This interest ensured that the Parallel Roads, and Glen Roy in particular, featured prominently in the development of geological science.
Interest in the Parallel Roads continues to this day, both among earth scientists intrigued by the dramatic geological and geomorphological processes that shaped the landscape, and among modern travellers and tourists attracted by the natural wonder of the landforms. Darwin made his "Gigantic Blunder" by believing that the shorelines were of marine origin, rejecting Agassz's (1840) Glacial theory, postulating shorelines being cut by freeze-thaw processes of lake ice, during the maximum extent of glacial ice in the climatic reversal known as the Younger Dryas / Greenland Stadial 1 or locally the Loch Lomond Readvance. Four decades after his 1839 paper, Darwin conceded that he was incorrect shortly before his death. However, he had conceded that he was embarrassed by "that confounded paper of mine" as early as 1861, in letters to Thomas.F.Jamieson, quoted by Jamieson (1863; 1892).