MACKIE — THE PAEALLEL EOADS OF GLEN EOT. 129 
visible. . . . Admitting, then, that the corroding action of the waters 
of the Spean and Eoy, operating on an alluvium at the exit of the 
Lochy, had, by destroying a portion of the barrier, discharged that 
portion of the lake which stood above the second line of Glen Eoy, 
a vertical distance of 82 feet, we have still left standing the other 
barriers, of the existence of which we cannot doubt, although their 
places cannot be precisely assigned. By what operation, then, were 
these lowered ? If by any causes of a nature similar to those which 
we see in daily action on the surface of the earth, it must have been 
by the flowing of rivers upon them. Thus the flow of the Ness and 
the Spey towards the sea might have lowered the land in these 
directions to their present level, and thus the exit of Loch Shiel 
might have destroyed the barrier to the west; while the repeated 
failures of the supposed barrier at the mouth of the Lochy had, in 
the meantime, produced the complete drainage of Glen Eoy and Glen 
Gloy, and, with the exception of Loch Laggan, that of the Spean." 
Macculloch himself felt the difficulties he had to contend with, and 
these he puts forward so openly, so honestly, and so undisguisedly, 
that we feel that his facts at least are carefully-gathered trutlis, and 
that we can depend upon them. "I know not," he frankly says, 
" that the direct arguments which have been here stated are sufficient 
to prove that hypothesis, respecting the ' lines ' of Glen Eoy, which 
appears to be the best founded ; or whether, combined with these 
indirect ones, which prove the impossibility of the two others, and 
the high improbability of the third, they may be held sufficient to 
establish its truth. I have, however, shown that although it still 
labours under unexplained difficulties, no physical impossibility is in 
any way opposed to its superior probability ; we may therefore admit 
its claim for the present, at least so far as to justify us in examining 
the geological consequences likely to result from it." 
Moreover, IMacculloch distinctly saw that the causes he had as- 
signed for the appearances in Glen Eoy were attended by conse- 
quences materially affecting the notions which had been, with every 
appearance of reason, entertained relative to the ancient state and 
posterior changes of the great Caledonian valley. " It is conceived," 
he says, " by many persons that Scotland was once entirely or par- 
tially divided in this place by the sea, the highest elevation of the 
present land being 90 feet. By the constant descent and accumula- 
tion of alluvium from the mountains, it is supposed that the dams 
have been formed which now separate Loch Oich both from Loch 
VOL. VI. 
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