MUIR GLACIER 25 



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. n. 2 



1 Sixteenth Ann. Rept. U. S. Geol. Survey, part I, pi. LXXXVI, 1896. 

 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 



