Casella’s thermometers on a piece of wood on one of the wet stones, clear of the ice, and it soon fell to 34 deg..  Probably the temperature had been somewhat raised by the continued presence of three human beings and two lighted candles in the small cavern; and, at any rate, the cold of two degrees above freezing was something very real on a hot summer’s day, and told considerably upon my sisters, so that we were compelled to beat a retreat,—­not quite in time, for one of our party could not effect a thaw, even by stamping about violently in the full afternoon sun.

While we were in the cave, we noticed that the surfaces of the columns were covered by very irregular lines, marked somewhat deeply in the ice, and dividing the surface into areas of all shapes, a sort of network, with meshes of many different shapes and sizes.  These areas were smaller towards the edges of the columns; the lines containing them were not, as a rule, straight lines, and almost baffled our efforts to count them, but, to the best of my belief, there were meshes with three, four, and up to eight sides.  The column which stood clear of the rock was composed of very limpid ice, without admixture of air; but the cascades were interpenetrated by veins of looser white ice, and, where the white ice came, the surface lines seemed to disappear.  As we sat on the grass outside, arranging our properties for departure, my attention was arrested by the columnar appearance of the fractured edge of the block of ice which we had used at luncheon.  It was about 5 inches thick, and had formed part of a stalagmite whose horizontal section, like that of the free column, would be an ellipse of considerable eccentricity; and, on examination, 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.