a little valley to the northwest of
Glen Roy, with a single terrace. Loch Treig is designated by T., Loch
Lochy by L. O., Loch Arkeig by A., and Moeldhu Hill by M., while E.
indicates Loch Eil. The Great Glen of Scotland, through which the
Caledonian Canal runs, extends in the direction of L. O. and E. The
position of Ben Nevis is designated by N. The dotted area between N. and
M. marks the place occupied by the great glacier of Ben Nevis, when it
extended as far as Moeldhu; while the close continuous lines in front of
Loch Treig indicate the direction of the glacial scratches left across
Glen Spean by the glacier of Loch Treig, when it extended as far as the
eastern termination of the two upper terraces. It ought to be
remembered, in this connection, that the bottom of the valley of the
Spean, as well as that of Glen Roy, is occupied by loose materials,
partly drift, that is, materials acted upon by glaciers, and partly
decomposed fragments of rocks brought down by the torrents, greatly
impeding the observation of the polished surfaces. The river-bed is cut
through this deposit, and here and there through the underlying rock.
Besides the parallel roads, there are also peculiar accumulations of
loose materials in Glen Roy and Glen Spean, more particularly connected
with the lowest terrace, which Mr. Darwin and Professor Jamieson have
shown to be little deltas formed during the existence of the lake of
Glen Roy at the bottom of the gullies intersecting the shelves of the
upper roads. The outlet for the water at the period during which the
second terrace was formed, not known when I visited Glen Roy, has been
discovered by Mr. Milne-Holme, and also observed by Professor Jamieson.
During the formation of the upper terrace, the waters escaped through
the westernmost tributary of the River Spey, in the direction of the
northeast corner of the wood-cut, and during that of the lowest terrace,
at the eastern end of Loch Laggan, also through the valley of the Spey.
The state of preservation of the parallel roads is such as to prove that
no disturbance of any importance can have taken place in the country
since they were formed. Far from believing, therefore, that these
remarkable shelves are ancient sea-beaches, I am prepared to maintain,
that, had the area occupied by them been submerged only for a few days,
under an ocean rising and falling for several feet with every tide, no
vestige would have been left of their former existe