402 MR MILNE ON THE PARALLEL ROADS OF LOCHABER. 



this, he ought to have shewn how circumstances caused that anomaly at Glen 

 Roy and its adjoining vaUeys. 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 

 KUfinnin, 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 existing along our coasts, pre- 

 sent a very mai-ked contrast with the Lochaber shelves. If these shelves had 

 been formed by the sea, it wUl, 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 

 teiTaces which occur along our coasts. 



5. If the Lochaber roads were fonned 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 mUes, 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 BlackwaU 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 fonned by arms of the sea, 

 ought all gi-adually 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 readUy 

 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, wiU also spread out more completely the detritus washed down into 

 it. In a 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 



