530 J. R. Dakyns — The Parallel Roads of Glen Roy. 



deep gill, which it meets just below the junction of the two branch 

 gills, and started at once again on the opposite side ; no talus con- 

 cealed the road ; it is cut out of the solid rock. A subordinate road 

 which occurs a little further north between the two ordinary top 

 roads was also seen to coincide with and, in fact, to be a rock feature. 



I was satisfied : I went no further : I had had two clear sections 

 of the two best-marked roads, one of each : the roads are, at all 

 events in some cases, cut out of the solid rock. It is reasonable 

 to conclude that where they appear to be confined to superficial 

 detritus, it is because the rock shelf is hidden by said detritus, which 

 has, in fact, accumulated along the road just because it is a shelf. 

 It is noteworthy that whereas the roads on the east side of Eoy, 

 where being free of detritus they are seen to form rock shelves, are 

 wide enough to allow two carts to pass each other. On the west 

 side where encumbered with debris they are no broader than a good 

 sized foot-path. 



The roads, though sensibly parallel and horizontal, are not abso- 

 lutely so ; for, according to the measurements of the Ordnance Sur- 

 veyors, the first road in Glen Eoy varies in elevation from 1144 to 

 1155 feet above the sea, the second from 1062 to 1077, and the third 

 from 850 to 862. Such variation in height would necessarily be 

 caused by the unequal accumulation of debris on the original shelves. 



It is right to say that there is an error in the mapping of the 

 roads on the One-inch Ordnance Map, Sheet 68 : on the map the top- 

 most road is represented as crossing the big two-grained gill just 

 below the bifurcation ; it really is considerably higher up, while it 

 is the second or middle road which crosses the gill at the fork. 



Diagram showing the profile of the mountain side with the three roads, the two 

 highest, Nos. 1 and 2, well marked, and the lowest, No. 3, not so well marked, 

 as seen by an observer looking up Glen Eoy. 



I have not seen the places where, as Mr. Darwin 1 observes, the 

 shelves entirely disappear on crossing the part of the mountains in 

 which the base-rock is exposed ; but I would ask whether the rock 

 1 Quoted by Sir John Lubbock, Quart. Journ. Geol. Soc. vol. xxiv. p. 84. 



