D. MILNE HOME ON THE PARALLEL ROADS OF LOCHABER. 605 
The foregoing localities for detritus are chiefly at places considerably above 
the level of the shelves, so that at the required levels, there were materials in 
abundance suitable to form blockages. 
In the bottoms of the valleys, the accumulations of drift are of course much 
ereater than near the tops or ridges of the hills. Scaurs or cliffs of detritus, 
in some places 80 feet high, are in all the ravines on the sides of the adjoining 
hills. On the Laire Burn (to the west of Loch Treig) there are scaurs of 
coarse clay and gravel nearly 300 feet high. 
But is it likely that the detritus was deposited only on the tops or ridges 
of the hills, and in the bottoms of the valleys, and not also in what are now 
the hollows between the hills? Is it not quite as likely that the detritus, 
originally filled or occupied these hollows, so that originally no valley existed, 
at all events valleys of the depth which now exist ? 
Mr Darwin argues (page 53 , “that the Valley was once partly or entirely 
jilled up, to the height of the shelves, by drift materials.” To a certain extent I 
concur in this opinion. I think that the more the valleys were filled, the better 
we can understand how the very tops of the hills, as well as their sides, should 
have been covered, and should be still covered, by gravel and sand. 
On these grounds, I submit, that in the Lochaber district, ample materials 
existed for forming detrital blockages of the Glens, to keep in and keep up the 
lakes to the heights which their shelves indicate. 
4. When the land began to rise up out of the ocean, so that extensive 
portions of country became exposed, what would happen? That lakes would 
be formed at high levels, and be kept at these levels by detritus, is consistent 
alike with reason and fact. 
There are even yet in this district of the Highlands, numerous lakes at 
high levels, kept in by detrital matter. Last October I visited Loch Earba, 
a lake about 4 miles in length, situated about 2 miles to the South of Loch 
Laggan. That lake is at a height of about 1120 feet above the sea, and is kept 
up by a mass of detritus, through which the stream from the lake has cut its 
way to Loch Laggan. There happens to be a quarry or pit near the point 
of discharge, for getting from it gravel and boulders, to be broken into 
road metal, which shews the character and thickness of the detritus at this 
place. The waters of Loch Earba, however, formerly stood higher than at 
present, as is shown by a horizontal beach line about 30 feet above the present 
level of the lake, which runs for several hundred yards at its north end along 
its west bank. This beach line is traceable also near the south end. 
In the same district of Lochaber, there are other two or three lakes at even 
greater heights, which I was informed, though I have not visited them, are in 
like manner kept up by detritus. 
There are numerous lakes at lower levels, also kept in by detrital 
