Mr Milne on the Parallel Roads of Lochaber, 359 



mounds of blocks which occur at the mouth of the valley of Loch 

 Treig, where it joins Glen Spean. It seemed to me (he adds) as if 

 I wore looking at the numerous moraines of the neighbourhood of 

 Tines, in the valley of Chamounix." These terraces of blocks, thus 

 likened to moraines, are, I presume, the accumulations of blocks on 

 the lowermost horizontal shelf, which is very conspicuous at the en- 

 trance to Loch Treig on both sides of the valley. On this shelf there 

 are multitudes of blocks, just as in many other parts of the valleys, 

 where this shelf and the others occur. But this fact is perfectly con- 

 sistent with the theory that these shelves were formed by water, and, 

 indeed, can be explained on no other, when it is considered that they 

 form at Loch Treig, as at every other place, a line absolutely hori- 

 zontal, — a quality which, I presume, no moraine ever possesses. 



The only place where I observed an accumulation of blocks, at all 

 resembling a moraine, is on the east side of Glen Spean, near a place 

 called the Rough Burn, about three or four miles to the north of 

 Loch Laggan. The accumulation is enormous. Blocks are piled 

 over each other to such a height as to render the general surface of 

 the moor, over a wide extent, quite undistinguishable. This accu- 

 mulation occurs not at the mouth of any valley. On the contrary, 

 tho hills near these blocks on the east side, are not much furrowed 

 oven by mountain torrents, and present a somewhat steep and high 

 wall face to the west. On looking round for any possible explana- 

 tion of tho occurrence in this spot of so unusual a quantity of boul- 

 ders, consisting almost entirely of gray granites, whilst the rocks on 

 which they lie are different. I could not help noticing that the valley 

 on the opposite or west side presented an opening or depression, 

 though at the distance of 2 miles. This opening is the outlet of Loch 

 Treig, and bearing about WSW. by compass. The appearance of 

 the locality at once suggested the probability that the blocks had in 

 some way issued through this opening, and had been transported 

 across the valley to their present situation, where their farther pro- 

 gress was arrested by the lofty hills forming here the east side of 

 Glen Spean. 



I have already stated reasons for thinking that no glacier issued 

 from Loch Treig. Tho only alternative seems to be the agency of 

 water. 



I proceed now to show that the lake theory of the Lochaber 

 shelves, and tho principles on which I have endeavoured to account 

 for the formation of lakes, and the eventual depression and drainage 

 of them, are not inconsistent with any established geological truths, 

 — but, on the contrary, receive support from collateral consider- 

 ations. 



1 . The first circumstance which I shall notice, is the occurrence 

 of Parallel Roads in other valleys similar to those of Lochaher, the 

 formation of which can be attributed to no other cause than lakes. 



I have the less hesitation in availing myself of this argument, 



