Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/328

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about four miles in length and one or more in breadth, being bounded on two opposite sides by high mountains. From them descend two streams which unite about the middle of the valley to form the Roy. From this junction the water flows with a moderate velocity for a space of two miles, when the glen suddenly contracts and terminates in a rocky hill of low elevation. The water, forcing its way for some distance through a narrow pass between approaching rocks, enters into a second glen, which I shall distinguish by the name of the lower Glen Roy. It is in this latter glen that the phenomenon of the roads is chiefly to be seen, nor on entering the upper from the lower one would it be suspected that any similar appearance existed in it. A line however may be observed on the left hand extending upwards from the junction which forms the Roy, along the face of a low hill towards the elevation in which Loch Spey lies. A careful examination of this line by the spirit level shows it to consist of a level narrow terrace, which if prolonged eastward would cut the perpendicular above Loch Spey, and if continued westward would meet the summit of the flat rock that forms the division between the higher and lower Glen Roy. It will speedily be seen that this summit is on a level with the uppermost of the lines in lower Glen Roy, and that the terrace which I have now described is in fact a prolongation of that line. It is necessary to remark that no other terrace or line is found in the upper valley.[1]

The flat rock already mentioned as forming the gorge of lower

  1. The map, Pl. 20, is copied from Arrowsmith's work, and contains various lines supposed to be seen in the adjoining vallies. I have retained them in all the places which I had no opportunity of examining, without intending to be responsible for their existence. Where they did not agree with my own observations I have without scruple omitted or altered them.