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MR MILNE ON THE PARALLEL ROADS OF LOCHABER. 403 
be scarcely if at all removed, and will thus form projecting buttresses nearly flat 
in their upper surfaces, and presenting steep escarpments towards the lake. 
Now, applying these two principles of tidal action to the shelves of Lochaber, 
we seek in vain for any actual cndentation into the sides of the hills. The shelves 
consist entirely of buttresses which stand out from the sides of the mountains; and 
these buttresses, so far from sloping at an angle little less steep than that of the 
sides of the mountains (which would be the case with the sea), form flats or ter- 
races which deviate in general very slightly from the horizontal. 
7. If the shelves were formed by the action of the sea, they should be most dis- 
tinct at places where the hill sides had been most exposed. 
Thus, on the north and north-west sides of Craig Dhu, and on the west side 
of Bohuntine, where there must, on Mr Darwin’s theory, have been an open ex- 
panse of ocean, the shelves should have been most distinct. But at these places, the 
three highest shelves are entirely absent ; the fourth alone is visible, though, being the 
lowest, it must have been less exposed. It is quite anomalous, on the marine 
theory, that the shelves should not have been formed where the force of waves 
and of tidal currents must have been greatest, and that they should have been 
most distinctly formed in the higher and more sheltered parts of Glen Roy. 
The hills at the mouth of Glen Roy seem rather to indicate that the highest 
shelves had not been formed on them,—the very reverse of what might have been 
anticipated if Mr Darwin’s views are sound. If they had been formed, they would 
not have been obliterated, as is manifest from the perfect preservation of shelf 4 
on Craig Dhu and Bohuntine. 
8. Having stated these objections to the theory of Mr Darwin, I proceed to 
consider his objections to the theory, that the shelves were formed by lakes. 
These objections resolve entirely into the difficulty of explaining the disap- 
pearance of the barriers, which must have dammed back the water in the valleys. 
But it would be no good reason for rejecting an explanation founded on the exist- 
ence of barriers, even though we could not very clearly account for the disappear- 
ance of them, provided that there is direct and conclusive evidence that such bar- 
riers existed. Now, I conceive that there is such evidence furnished by the con- 
siderations before referred to. 
Let us examine, however, the alleged difficulty of explaining, how the waters 
could have been dammed up in the valleys to the height of the several shelves. 
Shelf 2 is distinctly marked on both sides of Glen Roy, down to a certain 
point,—and also on both sides of Glen Collarig, down to a certain point. At this 
period, the water flowed from the east end of Glen Roy into the valley of the 
Spey. Something must have existed, therefore, in both glens at the points above 
referred to, to prevent the extension of the shelf westward. 
Shelf 3, in both glens, extends a little more to the west than shelf 2. We 
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