he does not mention whether this character prevails throughout the whole
212 vertical feet--a most important consideration; nor does he state
whether these rocks are polished or scratched, as might have happened even
to a considerable depth beneath the water (Mem. great icebergs in narrow
fiords of T. del Fuego (522/9. In the "Voyage of the 'Beagle'" a
description is given of the falling of great masses of ice from the icy
cliffs of the glaciers with a crash that "reverberates like the broadside
of a man-of-war, through the lonely channels" which intersect the
coast-line of Tierra del Fuego. Loc. cit., page 246.)) by the action of
icebergs, for that icebergs transported boulders on to terraces, I have no
doubt. Mr. Milne's description of the outlets of his lake sound to me more
like tidal channels, nor does he give any arguments how such are to be
distinguished from old river-courses. I cannot believe in the body of
fresh water which must, on the lake theory, have flowed out of them. At
the Pass of Mukkul he states that the outlet is 70 feet wide and the rocky
bottom 21 feet below the level of the shelf, and that the gorge expands to
the eastwards into a broad channel of several hundred yards in width,
divided in the middle by what has formerly been a rocky islet, against
which the waters of this large river had chafed in issuing from the pass.
We know the size of the river at the present day which would flow out
through this pass, and it seems to me (and in the other given cases) to be
as inadequate; the whole seems to me far easier explained by a tideway than
by a formerly more humid climate.

With respect to the very remarkable coincidence between the shelves and the
outlets (rendered more remarkable by Mr. Milne's discovery of the outlet to
the intermediate shelf at Glen Glaster (522/10. See Letter 521, note.)),
Mr. Milne gives only half of my explanation; he alludes to (and disputes)
the smoothing and silting-up action, which I still believe in. I state:
If we consider what must take place during the gradual rise of a group of