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

U. MILXE H()ME OX THE TARALLEL ROADS OF LOCHABER.
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(iver this district of the Highlands, detritus formerly existed to such an extent ,
tliat blockages might have been formed by it, to keep up lakes existing in the
Fig. 7. (Seep. 608.;
Section showing lake siiiiposeJ to have formerlj- existed near llonessie.
country to the requisite height ; and (2.) That there are many cases now in the
Highlands, of lakes kept up in this manner; (3.) That lakes have subsided, and
even drained altogether, by the -wearing doAATi and removal of detrital blockages
throuo-h the action of rivers.
Fig. 8. (See p. 608.);
Section showing the same spot near Monessie after the lake was drained, by the
River Spean having cut through the detritus and subjacent rocks.
.5. If these views be applied to the Parallel Eoads in the respective glens,
they will be found sufficient to explain by Avhat means these Roads stojDped
at the places marked on the map.
(1.) As the two shelves of Glen Gluoy appear only in the upper part of the
glen, some blockage must have existed at its mouth. I shall revert to this Glen
Gluoy blockage in a subsequent part of the paper when discussing the blockage
of the Great Glen. iSIeanwhile, I would refer to a peculiarity in Glen Gluoy, that
the upper shelf extends farther down the glen than the lower shelf. A B in
fig. 9 is the hill forming one side of the valley on which the shelves are
marked, C C is the highest shelf, and D D the lowest. The greater extension of
the upper shelf may be accounted for, by supposing that the detrital blockage E,
sloped in the way sho%\ni in the figure, which is the usual form of a lake bottom.
(2.) It is not difficult to understand how or why the blockage changed posi-
tion and level, if it teas detritus. There are, in all the Glens, multitudes of