it turned out that the surface areas, which varied in size from a
large thumb-nail to something very small, were the ends of prisms
reaching through to the other side of the piece of ice, at any rate in
the thinner parts, and presenting there similar faces. Not only so,
but the prisms could be detached with great ease, by using no
instrument more violent than the fingers; while the point of a thin
knife entered freely at any of the surface lines, and split the ice
neatly down the sides of the prisms. When one or two of the sides of a
prism were exposed, at the edge of the piece of ice, the prism could
be pushed out entire, like a knot from the edge of a piece of wood. In
some cases there seemed to be capillary fissures coincident with the
lines where several sides of prisms met. Considering the shape of the
whole column, it is clear that the two ends of each prism could not be
parallel; neither was one of the ends perfectly symmetrical with the
other, and I do not think that the prisms were of the nature of
truncated pyramids. On descending again, I found that the columns
were without exception formed of this prismatic ice, either in whole,
as in the clear column, or in part, as where limpid prisms existed
among the white ice which ran in veins down the cascades. In the free
vertical column the prisms seemed to be deposited horizontally, and in
the thicker parts they did not pass clear through. We carried a large
piece of ice down to Arzier in a botanical tin, and on our arrival
there we found that all traces of external lines had disappeared.

This visit to the glacière was on Saturday, and on the following Monday
I determined to go up alone, to take a registering thermometer, and
leave it in the cave for the night; which, of course, would entail a
third visit on the next day. Monday brought a steady penetrating rain,
of that peculiar character which six Scotch springs had taught me to
describe as 'just a bit must;' while in the higher regions the fog was