, and they leave no doubt upon the mind that Glen Spean was at
one time filled by a great glacier. To the disciplined eye the aspect
of the mountains is perfectly conclusive on this point; and in no
position can the observer more readily and thoroughly convince himself
of this than at the head of Glen Glaster. The dominant hills here are
all intensely glaciated.

But the great collecting ground of the glaciers which dammed the glens
and produced the parallel roads, were the mountains south and west of
Glen Spean. The monarch of these is Ben Nevis, 4,370 feet high. The
position of Ben Nevis and his colleagues, in reference to the
vapour-laden winds of the Atlantic, is a point of the first
importance. It is exactly similar to that of Carrantual and the
Macgillicuddy Reeks in the south-west of Ireland. These mountains
are, and were, the first to encounter the south-western Atlantic
winds, and the precipitation, even at present, in the neighbourhood of
Killarney, is enormous. The winds, robbed of their vapour, and
charged with the heat set free by its precipitation, pursue their
direction obliquely across Ireland; and the effect of the drying
process may be understood by comparing the rainfall at Cahirciveen
with that at Portarlington. As found by Dr. Lloyd, the ratio is as 59
to 21--fifty-nine inches annually at Cahirciveen to twenty-one at
Portarlington. During the glacial epoch this vapour fell as snow, and
the consequence was a system of glaciers which have left traces and
evidences of the most impressive character in the region of the
Killarney Lakes. I have referred in other places to the great glacier
which, descending from the Reeks, moved through the Black Valley, took
possession of the lake-basins, and left its traces on every rock and
island emergent from the waters of the upper lake. They are all
conspicuously glaciated. Not in Switzerland itself do we find clearer
traces of ancient glacier action.

What the Macgillicuddy Reeks did in Ireland, Ben Nevis and the
adjacent mountains did, and continue to do, in Scotland. We had an
example of this on the morning we quitted Roy Bridge. From the bridge
westward rain fell copiously, and the roads were wet; but the
precipitation ceased near Loch Laggan, whence eastward the roads were
dry. Measured by the gauge, the rainfall Fort William is 86 inches,
while at Laggan it is only 46 inches annually. The difference between
west and east is forcibly brought