(IS054 4) 
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 Davin Mixng, Esq. 
(Read 1st 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 MacCuLLocu gave an elaborate description 
of them, in a paper read before the Geological Society of London. In the year 
1818, Sir Toomas Dick Lauper 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 Darwin, 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 RopEricxk I. Murcutson, 
Mr Lye, and Mr Horner, all 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 | 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. 5H 
