PRESSURE OF TIDAL GLACIERS 
217 
tidal glacier has been greatly overrated, and I discredit 
the supposed power of sea pressure to make important 
reduction of a glacier’s efficiency for erosion. 
The preceding pages were submitted in manuscript to 
several friends competent to consider questions in molec¬ 
ular physics. Some of them think the ability of the sub¬ 
glacial film to resist expulsion has been overestimated, and 
especially that the film should not be assumed to exist 
between the bed-rock and the abrading angles of rock 
particles held in the ice. If it be true that abrading par¬ 
ticles are in absolute contact with the bed, and if it 
be further true that there is no film between the same 
particles and the partly enveloping ice, then parts of the 
glacier (regarded as a body of ice and fragmental rock) 
are directly supported by the bed. However important 
the distinction may be with reference to a complete 
theory of glacial abrasion, it seems to have little bearing 
on the question of pressure as here considered. We 
may conceive the whole glacier to consist of infinitesimal 
vertical columns, some terminating on the bed and sup¬ 
ported by it, others resting directly on a capillary film of 
water and thus indirectly supported by the bed, and yet 
others terminating on a water stratum of supercapillary 
depth. The last are sustained in part only by the hydro¬ 
static pressure communicated by the water stratum, and 
are otherwise upheld directly by their coherent neighbors 
of the first and second groups, and through them, indi¬ 
rectly, by the bed. 
It is a corollary to the general conclusion of this section 
that the existence of a fiord — that is, of a glacial trough 
partly occupied by an arm of the sea— is not demonstra¬ 
tive of a relatively low base-level at the time of its excava¬ 
tion. In the regions of the Alexander Archipelago and 
Prince William Sound there is independent reason to 
think the base-level was relatively low when the glaciers 
