The. Flow of Glaciers .— Fpham. 23 
crystals with more or less clearly defined shear planes. Here 
the grains have been broken by excessive strains.” 
Figures 4 and 5 show horizontal slices of the Obergrindel- 
wald glacier, parallel with the veined structure. Figure 6 is 
a horizontal section from the Eismeer of the Untergrindel- 
wald glacier, taken from beneath the medial moraine. There 
the ice had a clear blue color, with no observable veining. 
Lastly, figure 7 is a vertical section from the Mer de Glace, 
with lines of shear planes, showing again very conspicuously 
how far even adjacent grains vary in size. 
Concerning Tyndall’s reference of the vein structure or 
lamination primarily to pressure more than to differential 
shearing motion, with corresponding modification of the 
granular structure as shown in the figures, these authors re¬ 
mark : “ In all cases, as far as our experience goes, the direc¬ 
tion of the veined structure, rather than being at right angles 
to the direction of greatest pressure, was such as would be 
produced by the shear the glacier undergoes in changing its 
shape, or rather the relative position of its parts, during its 
descent.” 
Ice frozen on the surface of a lake or river differs entirely 
from the granular ice of glaciers in having a prismatic 
structure, so that often by slow melting during the spring, 
with accompanying rains, it is divided into columns which 
only loosely cohere together. Gen. J. G. Totten described a 
most surprising instance of the rapid disappearance of the 
ice, about a foot thick, from lake Champlain during a single 
windy night, owing to this method of melting. The ice, he 
says, was “ a mere aggregation of vertical prismatic crystals, 
cohering only at points and along edges and narrow surfaces, 
as shown next morning by fragments on the shore.”* 
The granular structure is, therefore, a decisive proof that 
the underground ice strata found by Baron Toll in the New 
Siberia islands, and the similar ice formation of Eschscholtz 
bay and other localities in northwestern Alaska, compared by 
Dali to compacted hail as its peculiar texture is disclosed in 
melting, are, as Toll has well named them, “ dead and fossil 
glaciers.”f 
*Am. Jour. Sci., II, vol. xxvm, pp. 359-364, Nov., 1859. 
fSee the Am. Geologist, vol. xv, p. 258, April, 1895 ; vol. xvr, pp. 
314-316, Nov., 1895. 
