At all events, it is
evident that at some time posterior to this universal glacial period,
when the ice began to retreat, Glen Roy became the basin of a glacial
lake such as we now find in the Alps of Switzerland, where occasionally
a closed valley becomes a trough, as it were, into which the water from
the surrounding hills is drained. In such a lake no animals are found,
such as exist in any other sheet of fresh water, and this would account
for the absence of any organic remains on the terraces of Glen Roy. But
at first sight it seemed that this theory was open in one respect to the
same objection as the other. What prevented this sheet of water from
spreading east and west in Glen Spean? If it not only filled Glen Roy,
but extended to the southern side of Glen Spean immediately opposite
the opening of Glen Roy, what prevented it from filling the whole of
that valley also? In endeavoring to answer this question, I found the
solution of the mystery.
The bed of Glen Spean, through its whole extent from east to west, is
marked, as I have said, by glacial action, in rectilinear scratches and
furrows. This westward track of the main glacier is crossed transversely
near the centre of the valley by two other glacier-tracks cutting it at
right angles.
Pages:
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237