the ice in La Genollière, frozen into the remains of a column.

There was so very much to be observed on all sides, and the measurements
took up so much time, owing to the peculiar difficulties which attended
them, that I did not examine with sufficient care the curious floor of
ice through which we cut our way to the lower cavern. Neither did I
notice the roof of the cavern thus reached, which may be very different
from the shape of the upper surface of the floor composing it. If the
ice-wall goes straight up, and the roof is formed of the ice-floor
alone, then it is a very remarkable feature indeed. But, more probably,
the lower wall leans over more and more towards the top, and so forms as
it were a part of the roof. It is possible that, as the wall has grown,
each successive annual layer has projected farther and farther, till at
last some year very favourable to the increase of ice has carried the
projection for that year nearly to the opposite stones, and then an
unfavourable year or two would form the foot of the upper wall. This
seems more probable, from the loose constitution of the floor at the
point where it joins the stones, as if it were there only made up of
drift and débris, while the part of the floor nearer the foot of the
wall is solid ice. It has been suggested to me that possibly water
accumulates in the time of greatest thaw to a very large extent in the
lower parts of the cave, and the ice-floor is formed where the frost
first takes hold of this water. But the slope of the ice-floor is
against this theory, to a certain extent; and the amount of water
necessary to fill the cavity would be so enormous, that it is contrary
to all experience to imagine such a collection, especially as the cave
showed no signs of present thaw. The appearance of the rocks, too, in
the lower cave, and the surface of the ice-wall there, gave no
indications of the action of water; and there was no trace of ice among
the stones, as there certainly would have been if water had filled the