172 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 26, 



surface of the lake, while glacial scores running horizontally along 

 the faces of the rock were traced up to 1280 feet (by aneroid) *. 

 Not that I can affirm this to be their upper limit ; for on the moun- 

 tain, at the opposite side of the gorge, I found the scoring fade 

 away so gradually at these great heights, owing to the weathering of 

 the rock, that I was unable to satisfy myself where it ended, perched 

 boulders and rounded surfaces occurring much higher ; and even up 

 to the top, which I made out to be about 3055 feet above the sea, 

 the gneiss, although it runs in nearly vertical stratification (dipping 

 N.W. at an angle of about 70° or 80°), is nevertheless so free of any 

 loose fragments on its surface, and the ends of the strata are often so 

 rounded in outline, as to raise a suspicion that some denuding agent 

 has flowed over it at a period geologically recent. This absence of 

 fragments cannot be attributed to the effect of the rain or snow 

 gradually carrying them down ; for it so happens that some felspar- 

 porphyry is occasionally interbedded with the gneiss: one such 

 stratum passes over the highest point of the hill ; and this porphyry, 

 like similar beds lower down in the gorge, is covered with a quantity 

 of its own angular debris which has not been carried off by the 

 rains. If the gneiss, therefore, had disintegrated to any extent, its 

 debris ought still to be found lying on its surface like that of the 

 porphyry. 



As I have already said, the evidences of glacial action are very 

 plain up to rather more than 1000 feet above the lake, and 1800 

 feet above the sea ; and near the angle of the moimtain, between 

 Loch Treig and Corry Laire, I found at this great height moraine- 

 matter, consisting of debris of mica-schist, gneiss, quartz-rock, and 

 felspar-porphyry, forming a loose heap of stony rubbish, which the 

 rains, aided by the scraping of the sheep, had laid open to a depth of 

 12 or 15 feet. The stones were of all sizes, up to about 3 feet in length, 

 and many of them glacially striated. This moraine -matter may be 

 traced down the spur of the hill for a long way, increasing in breadth. 

 Corry Laire, I have no doubt, has also been occupied by a glacier ; and, 

 looking down, I observed in the bottom of the glen what appeared 

 to be moutonneed rocks, but had no time to visit them. 



Nowhere have I met with such impressive evidence of intense 

 abrading force as these rocks present all about the outlet of Loch 

 Treig. The rounded masses of tough gneiss are so extensive as to 

 form hills several hundred feet high, and so smooth and bare that, 

 over extensive areas, even the moss and heather have completely 

 failed to get a footing on their surface. The amount of mineral 

 matter that has been ground down testifies how lengthened the 

 period must have been during which the abrasion had gone on ; and 

 the preservation of the scores and scratches on the present surface, 



* These aneroid measurements have, of course, no pretensions to accuracy, 

 and their results are given merely as the best approximation I can offer ; yet I 

 believe they are nowhere so far from the truth as to disturb any of the con- 

 clusions drawn from them. Indeed, where I have been able to check them by 

 other data, they have turned out to be nearer the mark than might have been ex- 

 pected, being seldom 50 feet wrong. 



