that no one, familiar with the presence of the
numerous ice-seams parallel to the layers of snow in these upper regions
of the glacier, can doubt that they, as well as the _neve_, are the
result of frost. But be this as it may, the difference between the
porous ice of the upper region of the glacier and the compact blue ice
of its lower track seems to me evidence direct that at times the whole
mass must assume the rigidity imparted to it by a temperature inferior
to the freezing-point. We know that at 32 deg. Fahrenheit, regelation
renders the mass continuous, and that it becomes brittle only at a
temperature below this. In other words, the ice can break up into a mass
of disconnected fragments, such as the capillary fissures and the
infiltration-experiments described in my "Systeme Glaciaire," show to
exist, only when it is below 32 deg. Fahrenheit. If it be contended that ice
at 32 deg. does break, and that therefore the whole mass of the glacier may
break at that temperature, setting aside the contradiction to the facts
of regelation which such an assumption involves, I would refer to Dr.
Tyndall's experiments concerning the vacuous spots in the ice.

[Illustration]

Those who have read his startling investigations will remember that by
sending a beam of sunlight through ice he brought to view the primitive
crystalline forms to which it owes its solidity, and that he insisted
that these star-shaped figures are always in the plane of
crystallization. Without knowing what might be their origin, I had
myself noticed these figures, and represented them in a diagram, part of
which is reproduced in the annexed wood-cut. I had considered them to be
compressed air-bubbles; and though I cannot, under my present
circumstances, repeat the experiment of Dr. Tyndall upon glacier-ice, I
conceive that the star-shaped figures represented upon Pl. VII. figs. 8
and 9, in my "Systeme Glaciaire," may refer to the same phenomenon as
that observed by him in pond-ice. Yet while I make this concession, I
still maintain, that besides these crystalline figures there exist
compressed air-bubbles in the angular fragments of the glacier-ice, as
shown in the above wood-cut; and that these bubbles are grouped in sets,
trending in the same direction in one and the same fragment, and
diverging under various angles in the different fragments. I have
explained this fact concerning the position of the compressed
air-bubbles, by assuming that ice, und