318 Dr. Mac Culloch on the Parallel Roads of Glen Roy. 



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. Fiom this junction the water flows with a mode- 

 rate velocity for a space of two miles, when the glen suddenly con- 

 tracts 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 dis- 

 tinguish 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 upper- 

 most 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.* 



The flat rock already mentioned as forming the gorge of lower 



* The map, PI. 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 exist- 

 ence. Where they did not agree with my own observations I have without scruple 

 omitted or altered them. 



