ltration is most copious and the winter cold has been accumulating
for the longest time. This view of the case is sustained by Elie de
Beaumont, who states his opinion upon this point as follows:--

"Pendant l'hiver, la temperature de la surface du glacier s'abaisse a un
grand nombre de degres au-dessous de zero, et cette basse temperature
penetre, quoique avec un affaiblissement graduel, dans l'interieur de la
masse. Le glacier se fendille par l'effet de la contraction resultant de
ce refroidissement. Les fentes restent d'abord vides, et concourent an
refroidissement des glaciers en favorisant l'introduction de l'air froid
exterieur; mais an printemps, lorsque les rayons du soleil echaffent la
surface de la neige qui couvre le glacier, ils la remenent d'abord a
zero, et ils produisent ensuite de l'eau a zero qui tombe dans le
glacier refroidi et fendille. Cette eau s'y congele a l'instant, en
laissant degager de la chaleur qui tend a ramener le glacier a zero; et
la phenomene se continue jusqu'a ce que la masse entiere du glacier
refroidi soit ramene a la temperature de zero."[H]

But where direct observations are still so scanty, and the
interpretations of the facts so conflicting, it is the part of wisdom to
be circumspect in forming opinions. This much, however, I believe to be
already settled: that any theory which ascribes the very complicated
phenomena of the glacier to one cause must be defective and one-sided.
It seems to me most probable, that, while pressure has the larger share
in producing the onward movement of the glacier, as well as in the
transformation of the snow into ice, a careful analysis of all the facts
will show that this pressure is owing partly to the weight of the mass
itself, partly to the pushing on of the accumulated snow from behind,
partly to its sliding along the surface upon which it rests, partly to
the weight of water pervading the whole, partly to the softening of the
rigid ice by the infiltration of water, and partly, also, to the
dilatation of the mass, requiting from the freezing of this water. These
causes, of course, modify the ice itself, while they contribute to the
motion. Further investigations are required to ascertain in what
proportion these different influences contribute to the general result,
and at what time and under what circumstances they modify most directly
the motion of the glacier.

That a glacier cannot be altogether compared to a river, although there
is a