Conceive such a mass of detritus having been removed, without great
projections being left on each side, in the very close proximity to
every little delta preserved on the lines of the shelves, even on the
shelf 4, which now crosses with uniform breadth the spot where the
barrier stood, with the shelves dying gradually out, etc. To my mind it
is monstrous. Oddly enough, Mr. Milne's description of the mouth of Loch
Treig (I do not believe that valley has been well examined in its upper
end) leaves hardly a doubt that a glacier descended from it, and, if the
roads were formed by a lake of any kind, I believe it must have been
an ice-lake. I have given in detail to Lyell my several reasons for
not thinking ice-lakes probable (520/2. Mr. Darwin gives some arguments
against the glacier theory in the letter (517) to Sir Charles Lyell;
but the letter alluded to is no doubt the one written to Lyell on
"Wednesday, 8th" (Letter 522), in which the reasons are fully stated.);
but to my mind they are incomparably more probable than detritus of
rock-barriers. Have you ever attended to glacier action? After having
seen N. Wales, I can no more doubt the former existence of gigantic
glaciers than I can the sun in the heaven. I could distinguish in N.
Wales to a certain extent icebergs from glacier action (Lyell has shown
that icebergs at the present day score rocks), and I suspect that in
Lochaber the two actions are united, and that the scored rock on the
watersheds, when tideways, were rubbed and bumped by half-stranded
icebergs. You will, no doubt, attend to Glen Glaster. Mr. Milne, I
think, does not mention whether shelf 4 enters it, which I should like
to know, and especially he does not state whether rocks worn on their
upper faces are found on the whole 212 [feet] vertical course of this
Glen down to near L. Loggan, or whether only in the upper part; nor does
he state whether these rocks are scored, or polished, or moutonnees, or
whether there are any "perched" boulders there or elsewhere. I suspect
it would be difficult to distinguish between a river-bed and tidal
channel. Mr. Milne's description of the Pass of Mukkul, expanding to a
width of several hundred yards 21 feet deep in the shoalest part, and
with a worn islet in the middle, sounds to me much more like a tidal
channel than a river-bed. There must have been, on the latter view,
plenty of fresh water in those days. With respect to the coincidence
of the shelves with the n