MUIR GLACIER 
2 5 
to understand that the comparatively weak and equally 
brittle material of glaciers may be still more susceptible 
to rupture by sudden strain. As the tension cracks inci¬ 
dental to the flow of glaciers are quickly welded, except 
near the surface, it would appear probable that earthquake 
cracks in the terrestrial parts of a glacier have no perma¬ 
nent effect of importance, but the case may be materially 
different in the parts encroaching on the sea. 
As heretofore known, the frontal wasting of Muir 
Glacier has been chiefly by melting below the water-line, 
and the ordinary bergs, produced by the shearing off of 
the overhanging upper portion, have been of moderate size, 
readily floating away. The greater bergs which stranded 
in the inlet after the earthquake may have been produced 
by cracks which divided the glacier from top to bottom. 
Reid Inlet . — Glacier Bay parts at its head into three 
branches (fig. 7). The westermost division, Reid Inlet, 
receives the Grand Pacific Glacier from the northwest, 
the Johns Hopkins from the west, and the Reid from the 
south, the three fronts circling in compact order about 
the western or northwestern end of the inlet. In 1899 
(as also in 1892) this was the region of most active berg 
formation, and on the day of our visit, June 12, the float¬ 
ing ice was packed so closely as to stop our progress — 
with a rowboat — and we succeeded in reaching only the 
Reid Glacier. With the use of a plane-table, a map was 
made of the lower end of Reid Glacier, and imperfect 
topographic sketches of the ends of the Johns Hopkins 
and Grand Pacific; and the data thus obtained were after¬ 
wards combined with the representations of the same dis¬ 
trict by Reid 1 and the Canadian Boundary Commission to 
produce the sketch map in fig. 11. 2 
1 Sixteenth Ann. Rept. U. S. Geol. Survey, part i, pi. lxxxvi, 1896. 
2 There is some confusion as to names of glaciers about the upper part of 
Glacier Bay. Muir, the explorer of the region, gave manuscript names, some 
