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 Boy, 

 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 JN~ess 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 truths, 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, Macculloch 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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