ere circumstances have been so favourable for the preservation
or formation of the terraces, a terrace could be formed quite plain for
three-quarters of a mile with hardly a trace elsewhere, we cannot argue,
from the non-existence of shelves, that water did not stand at the same
levels in other valleys. Feeling absolutely convinced that there was no
barrier of detritus at the mouth of Glen Roy, and pretty well convinced
that there was none of ice, the manner in which the terraces die out
when entering Glen Spean, which must have been a tideway, shows on
what small circumstances the formation of these shelves depended. With
respect to the non-existence of shelves in other parts of Scotland, Mr.
Milne shows that many others do exist, and their heights above the sea
have not yet been carefully measured, nor have even those of Glen
Roy, which I suspect are all 100 feet too high. Moreover, according to
Bravais (522/8. "On the Lines of Ancient Level of the Sea in Finmark."
By A. Bravais, Member of the Scientific Commission of the North. "Quart.
Journ. Geol. Soc." Volume I., page 534, 1845 (a translation).), we
must not feel sure that either the absolute height or the intermediate
heights between the terraces would be at all the same at distant points.
In levelling the terraces in Lochaber, all, I believe, have been taken
in Glen Roy, nearly N. and S. There should be levels taken at right
angles to this line and to the Great Glen of Scotland or chief line of
elevation.

Thirdly, the nature of the outlets from the supposed lakes. This appears
to me the best and newest part of the paper. If Sir James Clark would
like to attend to any particular points, direct his attention to this:
especially to follow Glen Glaster from Glen Roy to L. Laggan. Mr. Milne
describes this as an old and great river-course with a fall of 212 feet.
He states that the rocks are smooth on upper face and rough on lower,
but 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 channe