ese glens
constituted so many fiords, on the sides of which the parallel
terraces were formed. This theory will not bear close criticism; nor
is it now maintained by Mr. Darwin himself. It would not account for
the sea being 20 feet higher in Glen Gluoy than in Glen Roy. It would
not account for the absence of the second and third Glen Roy roads
from Glen Gluoy, where the mountain flanks are quite as impressionable
as in Glen Roy. It would not account for the absence of the shelves
from the other mountains in the neighbourhood, all of which 'would
have been clasped by the sea had the sea been there. Here then, and
no doubt elsewhere, Mr. Darwin has shown himself to be fallible; but
here, as elsewhere, he has shown himself equal to that discipline of
surrender to evidence which girds his intellect with such unassailable
moral strength.

But, granting the significance of Sir Thomas Dick-Lauder's facts, and
the reasonableness, on the whole, of the views which he has founded on
them, they will not bear examination in detail. No such barriers of
detritus as he assumed could have existed without leaving traces
behind them; but there is no trace left. There is detritus enough in
Glen Spean, but not where it is wanted. The two highest parallel
roads stop abruptly at different points near the mouth of Glen Roy,
but no remnant of the barrier against which they abutted is to be
seen. It might be urged that the subsequent invasion of the valley by
glaciers has swept the detritus away; but there have been no glaciers
in these valleys since the disappearance of the lakes. Professor
Geikie has favoured me with a drawing of the Glen Spean 'road' near
the entrance to Glen Trieg. The road forms a shelf round a great
mound of detritus which, had a glacier followed the formation of the
shelf, must have been cleared away. Taking all the circumstances into
account, you may, I think, with safety dismiss the detrital barrier as
incompetent to account for the present condition of Glen Gluoy and
Glen Roy.

Hypotheses in science, though apparently transcending experience, are
in reality experience modified by scientific thought and pushed into
an ultra experiential region. At the time that he wrote, Sir Thomas
Dick-Lauder could not possibly have discerned the cause subsequently
assigned for the blockage of these glens. A knowledge of the action
of ancient glaciers was the necessary antecedent to the new
explanation, and experienc