THE STEUCTUEE AJS’D MOTION OF GLACIEES, 
335 
in their communications for the present untouched, and confine ourselves to stating a 
few of the circumstances which appear to us to render the theory doubtful. 
1. It is not certain that the colds of winter penetrate to depths sufficient to produce 
the blue veins, which, it is affirmed, are “ an integral part of the inmost structure ” of 
the ice. Saussuee was of opinion that the frosts of winter did not penetrate to a greater 
depth than 10 feet, even at the summit of Mont Blanc, and Professor Foebes considers 
this opinion to be a just one. But if so, there would be some difficulty in referring to 
the fi’osts of winter the blue veins which M. Agassiz observed at a depth of 120 feet 
below the surface of the glacier of the Aar. 
2. It will be remembered that M. Guyot’s statement regarding the blue veins is, that 
he saw the mass of the glacier composed of a multitude of layers of white ice, separated, 
each from the other, by a plate of transparent ice. The description of Professor Foebes 
is briefly this : — “ Laminae or thin plates of transparent blue ice, alternate in most parts of 
every glacier with laminae of ice, not less hard and perfect, but filled with countless air- 
bubbles which give it a frothy semitransparent look.” But there is another form of the 
blue veins, already referred to, which consists in transparent lenticular masses imbedded 
in the general substance of the white ice. Horizontal 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 following measurements, taken on the spot, will give an idea of their varying dimen- 
sions ; — 
Fig. 7. 
2 3 4 3 
Dimensions. 
m. 
in. 
in. 
m. 
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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 gi’een spots exhibited by sections of ordinary 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 summer 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 
water^ and as those formed in the ensuing summer cannot, while summer continues, be 
