PARALLEL ROADS OF LOCHABER. 101 
pink-coloured Felspar pebbles which occur in Glen Spean, and there occa- 
sionally forming boulders, which are supposed by some of my friends to have 
been brought there by a glacier from Loch Treig. These pebbles I showed to 
Mr Cameron, and asked him if there were any rocks of the same kind in the 
hills adjoining Loch Treig. He replied, that he had never seen any in the 
Loch Treig hills, but that he had seen them about two miles to the west. 
Finding that I had not time to go to the head of the loch, I drew Mr 
CAMERON’S attention to the mound of detritus on which we had been standing. 
I had also previously shown to him similar mounds at the foot of Loch Treig, 
and asked him whether mounds of the same kind existed at the head of the 
loch? He said that there were such, a road having been cut through one of the 
mounds near his own cottage, which showed much sand and fine gravel in it. 
On walking back to the foot of Loch Treig, I ascertained by aneroid, that 
the detritus in several places on its north bank reached to a height of fully 200 
feet above the lake. 
If ever glacier had been formed in Loch Treig and flowed out of it, it 
must have been at a period antecedent to the time when detritus had been 
laid down on its banks. 
Not only is there detritus on both sides of Loch Treig, and bearing occa- 
sionally the impress of two water lines, but just below the foot of the loch 
where the river emerges from it, there are enormous masses of detritus, which, 
cut through by the River Treig and by its tributaries, exhibit vertical scaurs 
from 60 to 70 feet deep. On the top of this detritus, there are on the south side 
of the river, and close to the loch, two extensive flats evidently due to the 
action of a lake. The lowest seemed to correspond with the height of Shelf 
4, visible on the opposite side of the river. The Ordnance Survey Map, how- 
ever, makes it 10 feet higher. 
But the important fact is undoubted, that here, as well as at Corry N’Eoin, — 
both inside and outside of these Glens, from which glaciers are imagined to 
have flowed into Glen Spean,—-there is an enormous accumulation of detritus. 
It is upon this detritus, as all parties admit, that the “ Parallel Roads” have 
been impressed ; so that if glaciers ever existed in these glens and flowed out 
of them into the low country, it must have been at a period before the detritus 
was laid down, and the lake beaches formed. 
V. How the Detrital Blockages of Glen Gloy and Glen Spean were removed. 
a 
In my last Memoir, I ascribed the removal of the blockages to one cause, 
viz., the agency of streams flowing through the main valleys, and also of 
streams rushing down upon the detritus, from the steep sides of the mountains 
adjoining. 
VOL. XXVIII. PART I. 2C 
