Upon tracing these cross-tracks carefully, I became
satisfied, that, after the surrounding ice had begun to yield, after the
masses of ice which descended from the northern and southern slopes of
the mountains into Glen Spean had begun to retreat, and to form local
limited glaciers, two of those lateral glaciers, one coming down from
Ben Nevis on the southwest, the other from Loch Treig on the southeast,
extended farther than the others and stretched across Glen Spean.[C]
These two glaciers for a long time formed barriers across the western
and eastern extension of this valley, damming back the waters which
filled Glen Roy and the central part of Glen Spean.
Evidently the glacier descending from Loch Treig was the first to yield,
for, by the time the Glen Roy lake had sunk to the level of the lowest
terrace, the entrance to the eastern extension of the valley must have
been free, otherwise the water could not have spread throughout that
basin as we find it did; but it would seem that by the time the western
barrier, or the glacier from Ben Nevis, was removed, the sheet of water
was too far reduced to have left permanent marks of its outflow into the
Great Glen, except by disturbing and remodelling the large moraines of
the older Glen Spean glacier.
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