348* 



2. On the Theory of the Parallel Roads m the Glens of Loch- 

 aber. By Sir G. S. Mackenzie, Bait. 



Sir George Mackenzie read a paper on the Theory of the Pa- 

 rallel Shelves in the Glens of Lochaber, in which he first noticed 

 the objections to the theories that ascribed the origin of these ap- 

 pearances to fresh-water lakes, the barriers of which had been 

 destroyed at different periods ; and to the ordinary action of the 

 sea when the land was at a lower level than at present. The 

 causes supposed to have removed the barriers, in the first case, 

 being^ violent disruptions, the preservation of level and parallelism 

 is totally inconsistent with such operations. In the second case, 

 the shelves being- confined to the single locality of these glens, 

 while, supposing them to have been sea-beaches, the appearances 

 of such shelves should be frequent and to be seen every where; it 

 becomes necessary that the elevation of the land should have been 

 confined to a narrow locality, and to have exhibited a boundary 

 no where to be found. In this case, also, the elevation of the land 

 must have been sudden, otherwise the traces of the action of the 

 sea would have been seen continuous all over the sides of the glens. 

 Sudden elevation being therefore necessary, it is not at all pro- 

 bable that the levels and parallelism could have been preserved 

 so perfectly as to be in accordance with the curvature of the earth. 



Sir George alluded to the researches of Sir James Hall in re- 

 ference to the debacle or flood that appears to have passed over 

 the country ; and to the notions of Professor Agassiz, that ice, a 

 universal glacier, had produced the phenomena which had been 

 attributed to the debacle. He denied that these phenomena could 

 have been the effects of glaciers properly so called ; though, as 

 stated by him in a paper read last session, masses of ice may have 

 been, and most probably were, brought from the Arctic Reg-ions by 

 the debacle, and may have been arrested in the narrow passes 

 among the mountains, forming- temporary glaciers, if such an ap- 

 pellation may be applied to them, and producing effects not easily 

 accounted for without such assistance. Sir George then pointed 

 out a singularity in the localities of the Lochaber glens, in refer- 

 ence to the demonstrated course of the debacle, which had led him 

 to attribute to that catastrophe the formation of the shelves. The 

 openings of the glens face that course, and they turn towards the 

 north, so as to become nearly parallel to the Great Glen. The 

 highest summit level is between Glen Gluoy and Glen Roy, and 

 the other lower summit levels are between Glen Roy, Glen Spean, 



