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subsequently upheaved ; that there were pauses in the process of 
upheaval, during which these 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 Eoy. It would not 
account for the absence of the second and third Grlen Eoy roads 
from Grlen Grluoy, where the mountain flanks are quite as 
impressionable as in Grlen Eoy. It would not account for the 
absence of the shelves from the other mountains in the neigh- 
bourhood, 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 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. Eoy, 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 retreat of the lakes. Professor 
Geike has favoured me with a drawing of the Glen Spean shelf 
near the entrance to Glen Trieg. The shelf forms a belt round 
a great mound of detritus which, had a glacier followed the for- 
mation 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 Eoy. 
Hypotheses in science, though apparently transcending experi- 
ence, 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 
assigned 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 experience 
of this nature was not possessed by the distinguished writer just 
mentioned. The extension of Swiss glaciers far beyond their 
present limits was first made known by a Swiss engineeer 
named Yenetz, who established, by the marks they had left 
behind, their former existence in places which they had long 
