Glenroy

Glenroy, the valley of a stream in Lochaber, Inverness, flowing 15 miles to the Spean at Inveroy, opposite the eastern spur of Ben Nevis. The steep narrow valley through which the Roy runs is remarkable for having its slopes indented with three shelves, which are everywhere perfectly horizontal and parallel to each other, in each case the line on the one side of the glen corresponding exactly in elevation to that on the other. The granitic and metamorphic rocks, of which the mountains are composed, are covered with a greater or less thickness of angular fragments and earth, and an examination of the shelves shows that they are worn out of this soft alluvial coating. They almost invariably form a gentle slope from the hillside, and are from 3 to 30 feet wide. The protrusion of the rocky body of the mountain, and the furrows of mountain-torrents, break their continuity, but with these exceptions one or more of them may be traced along the whole valley. The highest, which is 1139½ feet above the sea-level, is easily followed from the watershed between the Roy and the Spey (which is at the same elevation) along both sides of the valley, as far down as the point at which the valley narrows above Glen Glaster. The second shelf is 80 feet lower, runs parallel with the first all round the head of the valley, and is continued farther down until it includes Glen Glaster. The third line is 212 feet lower than the second; it may be traced along both sides of Glenroy, and round the mouth of the glen into the valley of the Spean, whose sides, at the same elevation of 847 feet, are marked from within 3 miles of the river Lochy up nearly as far as Loch Laggan. Many attempts have been made to explain the origin of these remarkable shelves. Their forming somewhat level roads around the valley originated the popular notion that they were made for the convenience of the heroes whose exploits are sung by Ossian. Playfair, in 1816, supposed they were aqueducts for artificial irrigation. Macculloch believed them to be the shore-lines of fresh-water lakes, which gradually washed away their barriers, remaining for a longer space at the height of the various shelves. This view may now be regarded as accepted, with the additional suggestion of Agassiz that the barrier or dam keeping back the water was formed of glacier ice, the lake having lowered in level as the barrier gradually melted away. See Robert Chambers's Ancient Sea Margins (1849); Tyndall, in the Popular Science Review (1876); Macfadzean's Parallel Roads of Glenroy (1883); and A. Geikie's Scenery of Scotland (2d ed. 1887).