D. MILNE HOME ON THE PARALLEL ROADS OF LOCHABER. 615 
have a depth or thickness of hundreds of feet. These accumulations occur, 
wherever the range of the hills retires from the general axis of the valley, 
to produce a bay and a depression of surface. These hollows have been and 
are still filled with drift. Assuming that the whole of the “Great Glen” 
was so filled; the drift has subsequently been scoured out by powerful agents 
passing through it, leaving untouched the drift where sheltered in side bays 
and depressions. 
In the ravine of the Inverfarrigaig river (about three miles to the east of 
Foyers Hotel) there is a very interesting cliff of clay, rudely stratified horizon- 
tally, and full of well rounded pebbles and boulders, with thin horizontal 
seams of sand. The scaur extends for about 250 yards. It is about 50 feet 
in height. It is 120 feet above Loch Ness, I cannot doubt that this bed 
of drift has been part of the general accumulation which filled up the Great 
Glen.* 
These deposits, so long as they filled the Great Glen, would facilitate, in the 
districts adjoining, the formation of lakes, and ensure the retention of these lakes 
at high levels, because the rivers discharging from them would at first have small 
power to cut through the detritus. But with the lowering of the ocean level, the 
removal of detritus everywhere would increase with the steeper gradients of the 
rivers, and with the greater area on which rain would fall. Nowhere would the 
removal of detritus be so rapid as in the Great Glen, owing to the height and 
steepness of the mountains on each side. The removal of detritus would 
probably be greater at the west end of the Glen than at the east end, because 
of the greater height of the mountains at the west, and a larger supply there 
of rain. The reason why portions of the detritus remain at the east end is, that 
the hills there are lower in height, and more apart from the central line of the 
great valley, 
On these grounds I think that when lakes existed in Glens Gluoy and Roy 
at their respective heights, exceeding 1100 feet above the sea, there was detritus 
* In all the valleys adjoining or near the “Great Glen,” there are still enormous deposits of drift, 
much of which evidently has been removed by rivers. Thus, in a valley called Flichity (about 12 
miles S. W. of Inverness) drift covers the hill sides up to the height of 2000 feet ; and in that valley 
there are traces of horizontal terraces, on the sides of the valley, more than 100 feet above the bottom, 
with a blockage of drift, at the lower or east end of the valley, which before it was cut through by 
the River Nairn must have been the means of causing the valley to be filled with water. 
At Rosemarkie, a few miles N.E. of Inverness, which Mr Jouty of Inverness took me to visit, there 
are magnificent sections of boulder clay, forming cliffs about 300 feet high. If the adjoining hills are, as 
they seemed to be, from their shape, composed of the same material, this deposit reaches to a height above 
the sea of 800 or 900 feet. How far down below the sea-level this clay deposit goes, it is impossible 
to tell, but at Fort George on the opposite side of the Firth, about three miles distant, a bore was sunk 
100 feet in the same sort of clay, without reaching the bottom. Here then a clay deposit exists 
about 1000 feet in thickness. Judging from the beds of sand in the clay, and from the pebbles in 
it being in nearly horizontal lines, I had no doubt that this Rosemarkie clay bed was a water deposit. 
-_ 
VOL. XXVII. PART IV. (Z 
