342 Mr Milne on the Parallel Roads of Lochaher. 



These observations of Mr Stevenson, whose professional accuracy- 

 is undeniable, 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. Chambers of Edinburgh, who had a larger 

 spirit-level, and we never could detect any deviation from horizon- 

 tality. 



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

 the shelves, about which former observers have disputed. Mac- 

 CuUoch found by his barometric observations, that the Glen Gluoy 

 uppermost 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 

 assumption that these shelves are precisely on the same level. Sir 

 Thomas Dick Lauder mentions, however, that Mr M'Lean, the en- 

 gineer who assisted him, made the Glen Gluoy shelf 12 feet above 

 that in Glen Roy, whilst Sir Thomas himself made it 1 5 feet. Ac- 

 cording to the observations made by myself and Mr .Chambers last 

 September, the difference is much greater. By levelling, we made 

 it 29 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 it a second shelf, which the barometer shewed to be 

 200 feet, and the sympiesometer 213 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 infor- 

 mation. I allude to the fact, that most of the shelves are coinci- 

 dent with some summit level, so as to admit of the waters flowing 

 over that level as over a lip. Thus the uppermost shelf of Glen 

 Gluoy No. 1, in Sir Thomas Dick Lauder's Memoir, is (as he ex- 

 plains) exactly coincident with the water-shed ridge which divides 

 Glen Gluoy from Glen Roy, so that the waters (whatever they 

 were) which stood at that height and formed the beach No, 1, must 

 have flowed out at the head of Glen Gluoy into Glen Roy. In like 

 manner, the uppermost shelf in Glen Roy, No. 2 in Sir Thomas 

 Dick Lauder's Memoir, is (as he also mentions) exactly coincident 

 with the water-shed ridge which divides Glen Roy from the valley. 

 of the Spey ; so that the waters which stood in Glen Roy at No. 2 

 beach, must have flowed over the head of the Glen into Spey valley. 



