of rock, an idea which
might suggest itself to anyone who had not seen it, and I think it
probable that the amount of ice represented in the section of the cave
is not an exaggeration. We were unable to measure the whole length of
the wall in the lower cave, from the large number of blocks of stone
which had fallen at one end, and lay against its face. Probably, from
the nature of the case, it was not so long as the 72 feet of wall above;
but we measured 50 feet, and could see it still passing on to the right
hand as we faced it. In trying to penetrate farther along the face, I
found a wing of the brown fly we had seen in considerable abundance on
the ice in La Genolliere, 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 debris, 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,