MR MILNE ON THE PARALLEL ROADS OF LOCHABER. 397 



give you afterwards. The result, T think, leaves no doubt as to the perfect horizon- 

 tality of the ' roads.'' The glen is much more extensive, both as regards length 

 and breadth, than I anticipated, and the height of the roads above its bottom is 

 also very considerable, and any thing like a series of cross sections, referred to the 

 same datum, would be a work of very great magnitude ; a month, 1 should say, 

 would not complete it. The whole we have been able to do, therefore, is to test 

 the uniformity of the levels of the different roads, by viewing them with a good 

 instrument from sevei-al points, as was done by Sir Thomas Dick Laudee ; and, in 

 addition to this, a section was made along the middle road, where it is pretty well 

 defined from Glen Turret downwards, for a distance of nearly 3J miles, and 

 throughout that stretch, the road was found to be -perfectly horizontal." ... " If I 

 had seen that any thing further could be done, I would have left my assistants 

 for a few days longer ; they were there a week." 



These observations of .Mr Stevenson, whose professional acciiracy is undeni- 

 able, confirming, as they so completely do, the result of Sir Thomas Dick Lauder's 

 survey (and he, too, was aided by an engineer), leave no doubt in my mind, as to 

 the horizontality of the roads. It is scarcely necessary to refer to any farther 

 and weaker testimony on the subject. But it may be proper to add, that during 

 the two occasions when I visited Glen Roy, I had a pocket-level with me, which 

 I constantly used ; and that on the last visit I was accompanied by Mr R. Cham- 

 bers of Edinburgh, who had a larger spirit-level, and we never could detect any 

 deviation from horizontality. 



2. There is a point of some importance bearing on the theory of the shelves, 

 about which former observers have disputed. MacCulloch found by his barometric 

 observations, that the Glen Gluoy uppeimost shelf is 12 feet above the highest in 

 Glen Roy ; but he attributed this difference to errors of observation, and his 

 theory in regard to the formation of the shelves proceeds expressly on the assump- 

 tion, that these shelves are precisely on the same level. Sir Thomas Dick Lauder 

 mentions, hoAvever, that Mr M'Lean, the engineer who assisted him, made the 

 Glen Gluoy shelf 12 feet above that in Glen Roy, whilst Sir Thomas himself made 

 it 15 feet. According to the observations made by myself and Mr Chambers last 

 September, the difference is much greater. By levelling, we made it 2.9 feet ; by 

 joint barometric and sympiesometer observations, I made it 23 feet. 



3. Whilst on the subject of Glen Gluoy, I may mention that I discovered in 



I it a second shelf, which the barometer shewed to be 200 feet, and the sympie- 

 someter 21 3 feet, below the level of the one before referred to. I detected it first 

 immediately above the mouth of Glen Fintec. It is traceable on both sides of the 

 glen, and for several miles upwards. 

 4. There is a circumstance of great importance, in the theory of these roads, 

 on which I was so fortunate as to obtain farther information. T allude to the 

 fact, that most of the shelves are coincident with some summit level, so as to ad- 



