12 
ON THE STRUCTURE AND MOTION OF GLACIERS 
veins, already referred to, which consists in transparent lenticular 
masses imbedded in the general substance of the white ice. Horizon- 
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2: 
tal sections of these transparent lenses 
were exposed upon the surface of the 
Grindelwald glacier, and vertical sections 
of them upon the perpendicular sides of 
the water-courses, and upon the walls of 
the crevasses. The accompanying mea- 
surements (fig. 7), taken on the spot, 
will give an idea of their varying dimen- 
sions. Such masses as these here figured 
were distributed in considerable numbers 
through the glacier; they had all the 
appearance of flattened cakes, and the 
smaller ones resembled the elongated 
green spots exhibited by sections of ordi- 
nary roofing-slate cut perpendicular to 
the planes of cleavage. Now it appears 
mechanically impossible that a solution 
of continuity, such as that supposed, 
could take the form of the detached 
lenticular spaces above figured. 
3. The fissures to which the blue 
veins owe their existence are stated to 
be due to the motion of the glacier ; and 
as this motion takes place both in sum- 
mer and winter, it is to be inferred that 
the fissures are produced at both seasons 
of the year. Now as the fissures formed 
in winter cannot be filled with ice during 
that season for want of wader, and as 
those formed in the ensuing summer 
cannot, while summer continues, be 
frozen for want of cold, we ought at the 
end of each summer to have a whole 
year’s fissures in the ice. These fissures, 
which the ensuing winter is, according 
to the theory, to fill with blue ice, must, 
in summer, be filled with due water. 
Why then are they not seen in summer ? 
The fissures are such as can produce 
plates of ice varying “from a small frac- 
