402 MR MILNE ON THE PARALLEL ROADS OF LOCHABER. 2 
this, he ought to have shewn how circumstances caused that anomaly at Glen 
Roy and its adjoining valleys. But he has not shewn, and cannot shew, that the 
sides of the Glen Roy mountains, are in any respect different from those other 
highland mountains. Indeed, he has himself pointed out a similar beach line at 
Kilfinnin, in a glen towards Inverness. I take leave farther to doubt the sound- 
ness of Mr Darwin’s proposition, that the preservation of ancient beach lines is 
anomalous. The whole of Scotland, and I believe also of the British Islands, is 
begirt with lines of ancient sea beach. 
4. The ancient sea beaches, now alluded to as caste along our coasts, pre- 
sent avery marked contrast with the Lochaber shelves. If these shelves had 
been formed by the sea, it will, I presume, be admitted that, considering their 
great altitude, they are of much older date than beach lines at a lower level. If 
older, then they should be less perfect and entire. But the contrary is the case. They 
are incomparably more perfect and entire than any of the lowest ancient sea 
terraces which occur along our coasts. 
5. If the Lochaber roads were formed by the sea, the well-known actions of 
the tides, to which Mr Darwin refers, would have precluded the formation of 
them along lines absolutely horizontal. 
Mr Darwin refers to a case in South America, where, in 18 miles, the tidal 
wave rises at one place 20 feet higher than another in the same estuary. Nearer 
home, in the Bristol Channel, the sea rises at its head about 50 feet higher than 
at its mouth. 
The tide at Blackwall rises 12 feet higher than at Yarmouth. In the Firth 
of Tay, the tide rises at Perth 18 inches above the level at Newburgh. The tide 
at Alloa is said to rise 2 feet 9 inches above its level at Leith. At Glasgow, the 
tide rises 10 or 11 inches above its level at Greenock. On the Dee, the level of 
high water is, at Chester, 8 inches above what it is at Flint, near the mouth of 
the river, a distance of 11 miles. 
On this principle, the beaches of Lochaber, if formed by arms of the sea, 
ought all gradually to rise to the head of the Glens—narrowing, as these glens 
do, towards the head. But this is negatived by the fact. 
6. On more narrowly considering the effect of tidal action, it will readily 
occur, that the beaches formed by the sea must be materially different from those 
of a lake, in which there is no movement of the water at the sides, except such as 
is caused by winds common to both. In the case of the sea, there is not only a 
vertical rise and fall of water (which, on the west coast of Scotland, is from 8 to 
16 feet) twice in the 24 hours, but also a good deal of lateral current alternately in 
opposite directions. Hence the sea, whilst it will eat into the land more rapidly 
than a lake, will also spread out more completely the detritus washed down into 
it. Ina lake, on the other hand, which has no movements of water either ver- 
tical or lateral, the detritus deposited on the sides of a valley occupied by it, will 
