J. F. Campbell Collection > On the parallel roads of Lochaber

D. MILNE HOME OX THE PARALLEL ROADS OF LOCHABER.
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had formed an angle or projecting point when the lake existed. The old beach,
viz., Shelf 4, goe.s round the rock.
Jamiesox, in like manner as Professor Xicol, maintains tliat whilst the
"drift beds" repose on the scored and j)olished rocks, the rocks were scored
and polished while the land was covered with ice, the drift beds being deposited
dnriiig the subsequent submergence of the land. (Vol. x^iii., p.l64.)
The cj[uestion is, whether the ice-sheet alone could have polished and scored
the rocks in the peculiar positions in wliich they are sometimes found. Had
these smoothed and scored rocks been generally on the tops or ridges of hills,
there would have been less difficulty in ascribing these effects to a general ice-
sheet. But instead of being in these exj^osed positions, the smoothed and
striated rocks are most frequently in valleys : — and the wr^/vo^rcy the valley, the
\\r-
1. Gneiss Boulder, 8 feet high, 48 feet rouDd, on Shelf 4, above Inverlair House ; shelf here
about 60 feet wide. 2. A rock smoothed by some agent. 3. Gravel stratified, on which the shelf
was formed, forming a steep scaur about 50" feet high.
vwre remarkable is the smoothing and polishing. This is undoubtedly the case
in Glen Spean, at its narrowest parts between the Roman Catholic Chapel and
Inverlair.
It appears also that the heavy body which effected the sti-iations was, when
obstructed in its passage by a solid rock, capable of rising over it.
Now what would happen, when a body of land ice was so obstructed ? If the
rock did not break, the under part of the ice would i^robably be arrested, and
the upper part would, under the influence of the proiielling force, move on.
On the other hand, in the case of a body of ice floating, the buoj\ancy
of the ice, when obstructed, woidd enal)le it to rise up and over the obstruction.