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XXVII. — On the Parallel Roads of Lochaber, with Remarks on the Change of 

 Relative Levels of Sea^ and Land in Scotland, and on the Detrital Deposits in 

 that Country. By David Milne, Esq. 



(Read let March and 5th April 1847.) 



There are few questions in geology which have given rise to so many theories, 

 and so much speculation, as the origin of the parallel roads in the valleys of 

 Lochaber. 



In the year 1817, the late Dr MacCulloch gave an elaborate description 

 of them, in a paper read before the Geological Society of London. In the year 

 1818, Sir Thomas Dick Lauder read before the Royal Society of Edinburgh a 

 paper, full of equally interesting details. Both of these observers suggested, in 

 explanation of the shelves which mark the mountain sides of these valleys, that 

 they had been occupied by lakes, which, by earthquakes or other violent convul- 

 sions, had been drained. This theory was generally received, until, in the year 

 1839, Mr Dab WIN, so justly celebrated as a geologist, and an accurate observer, 

 published his views, and pronounced the shelves to have been formed by the sea ; 

 an opinion which, besides being rested on proofs derived from the locality, he en- 

 forced also by his observation of similar appearances in South America. 



Mr Darwin's opinion has received the assent of Sir Roderick I. Murchison, 

 Mr Lyell, and Mr Horner, aU successively Presidents of the Geological Society, 

 besides other geologists, both at home and abroad, who are justly regarded as 

 authorities in physical science. Relying on the soundness of their views, I confess 

 that when I went to Glen Roy, in the year 1845, it was with a strong conviction 

 that the lake theory was indefensible ; a view to which I was the more inclined, 

 from having studied certain marks along different parts of the Scottish coast, on 

 both sides of the island, which satisfied me that the sea had recently stood at a 

 much higher relative level than at present ; and that, in its recession, it had 

 formed, all round our coasts, shelves or beach lines, very analogous to those in the 

 Lochaber valleys. I had not been two days in Glen Roy, before I satisfied myself 

 that these views were inapplicable to the shelves in it and its associated valleys. 

 But I was unable, during my visit of 1845, to remain long enough to obtain evi- 

 dence of the manner in which the lakes had been dammed up, and eventually 

 drained. I therefore resolved to defer the farther consideration of the subject, 

 until I could pay a second visit. This I accomplished in September 1846, when 

 I spent a week in the examination. 



In the following paper, I shall attempt to explain my reasons for thinking 



VOL. XVI. PART III. 5 H 



