256 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 21, 



The space between the highest Glen Roy line and the one in Glen 

 Gluoy does not appear to have been so carefully ascertained. Sir 

 Thos. Lauder-Dick states it at 12 feet. Dr. Macculloch, who in this 

 case used a barometer, also makes it 12 feet ; but Messrs. Chambers 

 and Milne-Home found it to be fully 29 feet. There is a fainter 

 trace of a lower line in Glen Gluoy, which, according to Mr. Easton, 

 C.E., is 200 feet below the upper one. I find that a rough aneroid 

 observation of my own made the distance between them a few yards 

 more. Professor Rogers also made some measurements of the Glen 

 Gluoy lines, and found that neither of them corresponds with those 

 in Glen Roy, but I have not seen any detail of his results. 



The shelf in the gully near Kilfinnan is, according to the baro- 

 metrical measurement of Mr. Darwin, 40 feet above the highest Glen 

 Roy line. 



The Ordnance Survey having carried a line of spirit-levelling along 

 the Loch Laggan road from Dalwhinnie to Spean Bridge in 1858, I 

 availed myself of their bench-marks to test the height and horizon- 

 tality of the lowest line, which extends into Glen Spean. The bench- 

 mark on Roy Bridge is 308*97 feet above the mean sea-level at 

 Liverpool, or say, in round numbers, 309 feet. Prom this point I 

 carried a line of spirit-levelling up to the inner angle, or upper border, 

 of the terrace of the lowest Parallel Road on the west side of an ad- 

 joining eminence called Meal Deny, and found it to be 545 feet 

 above the Ordnance-mark on Roy Bridge. The terrace here is rudely 

 marked, and so obscure when one is upon it, that its upper outline 

 could not be ascertained within a foot or two ; I therefore took sights 

 to various parts of the line in the immediate neighbourhood where it 

 was best defined, namely, on Ben Chlinaig and on Bohuntine Hill, 

 and found that I could not anywhere safely make the upper rim of 

 the marking exceed the height I have mentioned. This then gives 

 (545 + 309) 854 feet above the mean level of the sea for the height 

 of the line in the neighbourhood of Roy Bridge. If Mr. Chambers's 

 height is above high water, this would just about correspond with 

 his statement. 



I next went to the delta at the mouth of the Rough Burn, which 

 is about six miles east from Roy Bridge, and found the upper border 

 of the same line there (which is distinctly marked on the west side 

 of that delta) to be fully 10 feet higher than an Ordnance bench- 

 mark on the road near it. This bench-mark is 851 feet above the 

 mean sea-level, which gives 861 feet for the height of the line. The 

 trace of the same line at Inverlaire, which is clearly seen from this 

 spot, seemed to be equally high. But the top of the terraces at the 

 end of Loch Treig was distinctly higher ; as nearly as I could ascer- 

 tain, they are about 885 or 888 feet. This fact I have mentioned in 

 a former part of this paper. 



The breadth or vertical height of the line on the delta of the 

 Rough Burn is about 6 feet, so that its lower border is higher than 

 the upper border of the same line in the neighbourhood of Roy Bridge. 



Assuming then the Ordnancc-levellings to be perfectly trustworthy, 

 this would seem to show that the lowest of the Parallel Roads rises 



