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THE POPULAR SCIENCE MONTHLY. 



road of Glen Roy in the same manner, he assumed that at a certain 

 point the level of this road the barrier which had been wasting 

 away held its ground for a sufficiently long time to form the road. 

 But, on the same principle, there would naturally have been a greater 

 number of roads in this glen, and additional roads in the other glens. 

 A weakness was thus admitted into the theory which was immediately 

 attacked by Mr. Darwin. He believed that the whole region had once 

 been covered by the sea, and that, in the upheaval of the earth, there 

 were pauses during which these roads were formed. But this would 

 not account for the sea being higher in one of the glens than in an- 

 other, nor for the unequal number of terraces by which the mountains 

 are belted. As soon as Mr. Darwin detected these fallible points, he 

 abandoned his theory. 



In 1847 the Dick-Lander hypothesis received new strength from a 

 discovery made by Mr. Milne-Home. There is a lateral glen, called 

 Glen Glaster, running eastward from Glen Roy, which had escaped 

 the notice of Sir Thomas Dick-Lander. Mr. Milne-Home entered this 

 glen, pursued a branch of it extending to the southeast, and came 

 upon a water-shed exactly level with the second Glen Roy road. On 

 the same theory as before, when the barrier should be properly re- 

 moved, the water in Glen Roy would sink to the second road, and the 

 surplus water would escape over the Glen Glaster water-shed into 

 Glen Spean. But this mode of explanation could not yet be accepted, 

 for there is scarcely a trace left of the immense quantity of detritus 

 that would have been necessary to form the barriers. Nor could the 

 detritus have been swept away by glaciers, for there have been no 

 glaciers in these valleys since the retreat of the lakes. 



At the time when Sir Thomas Dick-Lander was making his inves- 

 tigations, the action of ancient glaciers was not understood. The 

 subject had been pursued in Switzerland, but it was not till 1840 that 

 unmistakable marks of glacier-action were pointed out in Great Britain 

 by Agassiz. He visited'Glen Roy, and, having detected the traces of 

 glaciers, pronounced these to have been the barriers blocking up the 

 glens. This theory was afterward examined and confirmed by Mr. 

 Jamieson. " It was their ascription to glacier-action," says Prof. 

 Tyndall, " that first gave the parallel roads of Glen Roy an interest 

 in my eyes; and in 1867, with a view to self-instruction, I made a sol- 

 itary pilgrimage to the place, and explored pretty thoroughly the roads 

 of the principal glen." At different places he found that the effects of 

 the lapping of the water on the more friable portions of the rock are 

 still perfectly distinct. Several months ago he again visited the 

 place, prior to delivering a lecture upon the subject. The entire 

 ground was thoroughly explored, and the principal hills were found 

 to be intensely glaciated. The collecting-ground of these glaciers, 

 which blocked up the valleys, were the mountains south and west of 

 Glen Spean among others, Ben Nevis. These lofty mountains en- 



