MACKIE — THE PAEALLEL EOADS OF GLEN EOT. 
131 
fallacy, because the causes which were in operation to form a barrier 
of alluvial matter could not be at the same time causes of destruc- 
tion. Jf any causes were in action capable of forming a barrier 
of fine earthy deposit to the height of 927 feet above the bottom of 
Grlen Eoy, the same causes could not possibly act, at the same time, 
in producing "a slow waste" in the opposing barrier. Besides, 
taking the opposite view, that the lake, by the accumulation of its 
water pent in by the barrier, acquired weight enough to burst it, 
what has become of the remains of such a gigantic mound? It could 
not have been washed away totally, and not have left a wreck behind. 
MaccuUoch's acute mind saw, too, the difficulty of removing the other 
earth-barriers, which must have remained after the breaking down of 
this one; " and other causes," he adds, "which we know not where 
to seek, must be found to explain the removal of alluvia from points 
where they appear at present to be, on the contrary, accumulating." 
Such in the main are the natural features presented by Glen Eoy ; 
and such the excellent A'iews put forward by MaccuUoch. That the 
" parallel roads " have been formed by water action, and are in point 
of fact ancient lake-shores, few are or have been much inclined 
to doubt. But the difficulty has been, as we have said, to find the 
barriers whicli held up the lake. Macculloch lived before these days 
of glacial theories, and he looked for a solid barrier of rock or earth ; 
and it was naturally considered that if such a barrier had existed, 
some traces of its ruins should remain. Agassiz, some years since, 
suggested the possibility of the Glen having been blockaded by gla- 
ciers, but did nothing towards proving the case beyond giving out 
that suggestion. 
Glacier-action, however, would eliminate all these incongruities 
from MaccuUoch's theory. A wall or barrier of ice would melt away 
and leave comparably to a bank of earth but very little trace indeed ; 
this is the point Mr. Jamieson has taken up to investigate. Sir 
Charles Lyell has referred to the parallel roads of Glen Eoy, and to 
Mr. Jamieson's previous labours in that region, in his recent work 
' On the Geological Evidences of the Antiquity of Man,' but since 
the labours there referred to, Mr. Jamieson has communicated a 
valuable memoir on the subject to the Geological Society of London^ 
of such importance that it must attract attention whenever it is pub- 
lished in the Society's Journal. In it he gives the proofs of ancient 
ice-action which he has met with in the district, and even assigns the 
places of the glacier-barriers ; but, if we understand his meaning 
