400 MR MILNE ON THE PARALLEL ROADS OF LOCHABER. 
which belonged to Glen Spean, but also those which flowed out from Glen Glaster, 
comprehending Glen Roy, Glen Collarig, and Glen Gluoy. The Glen Glaster river- 
course discharged the waters of Glen Collarig, Glen Gluoy, and Glen Roy, whilst 
the Glen Gluoy stream discharged only the waters of one lake. Mr Darwin did 
not visit the Pass of Mukkul. If he had studied the appearances presented by it, 
and by those almost as strikingly exhibited at Glen Glaster, he would have found 
it impossible to deny that the waters which formed shelves 3 and 4 flowed down 
river-courses, and therefore could not be arms of the sea. 
His proposition is, “that the waters of the sea, in the form of narrow arms 
or lochs, such as those now deeply penetrating the western coast, once entered 
and gradually retired from these several valleys;’ and he adds, that after 
considering the ‘‘ several and successive steps of the argument, the theory of the 
marine origin of the parallel roads of Lochaber, appears to me demonstrated.” 
(P. 56.) LTregret that Mr Darwin should have expressed himself in these very 
decided and confident terms, especially as his survey was incomplete; for I ven- 
ture to think, that it can be satisfactorily established, that the parallel roads of 
Lochaber were formed by fresh water lakes. 
1. The first circumstance which I shall notice as fatal to Mr Darwin’s theory, 
is suggested by the fact last referred to, that the waters which formed the different 
shelves, must have jlowed out of the glens, and descended by river-courses to lower 
levels. 'The waters which formed No. 1 shelf in Glen Gluoy descended nearly 29 
feet by flowing into Glen Roy. The waters which formed No. 2 shelf in Glen Roy 
flowed in like manner into the valley of the Spey. The waters which formed 
No. 3 shelf were discharged over the head of Glen Glaster, down a slope of about 
212 feet in vertical height, into Glen Spean. Lastly, the waters which formed 
shelf 4 in Glen Spean, issued out of Loch Laggan by the ancient river-course at 
Mukkul. 
Now, any one of these cases is irreconcilable with the notion, that the shelves 
had been formed by arms of the sea. There is no such thing in nature as a river 
flowing out of an arm of the sea, to a lower level. 
Mr Darwin, as we have seen, admits that this coincidence of the shelves with 
water-sheds, must be in some way connected with their origin ; and, accordingly, he 
endeavours to give an explanation of it consistently with his theory. He says that 
these water-sheds are land straits, with sea on each side of them, and that they 
consist of littoral deposits or accumulations of matter formed by the opposition of 
tides. This opinion, however, is altogether inconsistent with the actual circum- 
stances of the case. In the first place, there is at these water-sheds, no accumu- 
lation of littoral deposits or detrital matter. They consist, generally, of bared 
rocks, forming sloping channels or water-courses. In the second place, there is no 
trace of water at the same level, on each side of these water-sheds. In the third 
place, when land straits are formed by the accumulation of matter from opposition 
of tides, it is not in situations like the heads of glens which narrow to a point, and 
