678 
PROFESSOR PRESTWICH ON THE ORIGIN 
without its difficulties but that they are fewer than those presented by the other 
hypotheses, while it will, I think, be found to meet some of the many of the objections 
which have been raised to both the lake theories. I regret that the time at my dis¬ 
posal did not allow me to see all the points I could have wished, but the various 
and accurate researches of previous observers have sufficiently supplemented the data 
required for my object. 
§ 6. Depth of the Ice-sheet in Lochaber: Extent of the Glaciation. 
It is not necessary to discuss the general glaciation of Scotland and the extent of 
its great ice-sheet. For our purpose it is merely needed to determine its dimensions in 
this and adjacent district. The observations relating to this subject are not so nume¬ 
rous—especially at heights—as could be desired, still they are enough to prove the 
vast thickness of the ice at the period of the great first glaciation. 
Mr. Maclaren, in his paper “ On Ground and Striated Rocks in the Middle Region 
of Scotland,”* mentions generally that the effects of ice abrasion in the range of moun¬ 
tains south of the Spean Yalley can be traced to a height of more than 2,000 feet. 
Mr. Milne Home states! that smooth rock-faces at the entrance to Loch Treig 
extend to the height of 1,680 feet; again, that there are ice-worn surfaces on the 
west and south sides of Craig Dhu at a height of 1,800 feet, and on the west side of 
hill N.E. of Rough Burn at 1,600 feet above the sea. He mentions also that he found 
at the head of Glen Roy rocks with them smoothed surfaces facing west, and lower 
down on the south side of Glen Ptoy, nearly opposite the Gap, other smooth surfaces at 
a height of 1,238 feet; on the west side of Glen Gluoy above Alterahary Farm at 1,300 
feet; on the hill between the latter and Glen Fintaig at 1,700 feet; in Glen Glaster 
pass facing west, and on the west side of the hill one mile east of Loch Treig, at 1,600 
feet.j In a later paper,§ quoting from a MS. of Mr. Jolly, he instances glaciated 
rocks on Ben Chlinaig facing Glen Spean at a height of 1,750 feet, and in the Lame 
Yalley at 1,600 feet. 
Dr. R. Chambers || noted an ice-abraded rock at the top of Glen Glaster with the 
smoothed side to the N.W. He refers also to many glaciated surfaces at from 1,700 to 
2,000 feet, but not at greater heights. 
Mr. Jamieson examined in particular Glen Treig and Glen Arkaig for evidence of 
glacial action at heights. At the entrance of the former he found ice-striae as high as 
1,280 feet above the level of the loch, or more than 2,000 feet above the sea, but is of 
opinion that ice action extended even higher. In Glen Spean he “ was struck with 
glaciation, then there would be no objection to place the “ roads ” at the end of the second period. In 
fact, it would be necessary, as the second glaciation must then have obliterated any “roads” of the first. 
* Edinb. New Phil. Journ., vol. xlvii., p. 161, 1849. 
f Trans. Roy. Soc. Edinb., vol. xvi., p. 412. 
+ Ibid., vol. xxvii., pp. 634-638. 
§ Trans. Roy. Soc. Edinb., vol. xxviii., p. 98. 
|| Edinb. New Phil. Journ., vol. liv., p. 254, 1853. 
