Ice-Caves of France and Switzerland

by G. F. Browne

On arriving at the entrance to the glacière, the end of a suggestive ladder is seen under the protecting trunks; and after one or two steps have been taken down the ladder, the effect of the cave below is extremely remarkable, the main features being a long wall covered thickly with white ice in sheets, a solid floor of darker-coloured ice, and a high pyramid of snow reaching up towards the uncovered hole already spoken of. The atmosphere of the cave is damp, and this causes the ladders to fall speedily to decay, so that they are by no means to be trusted: indeed, an early round gave way under one of my sisters, when they visited the cave with me in 1861, and suggested a clear fall of 60 feet on to a cascade of ice.[^[16]] There are three ladders, one below the other, and a hasty measurement gave their lengths as 20, 16, and 28 feet. The rock-roof is only a few feet thick in the neighbourhood of the hole of entrance.

ENTRANCE TO THE GLACIÈRE OF S. GEORGES.

The total length of the cave is 110 feet, lying NE. and SW., in the line of the main chain of the Jura. The lowest part of the floor is a sea of ice of unknown depth, 45 feet long by 15 broad; and Renaud tried my powers of belief by asserting that in 1834 the level of this floor was higher by half the height of the cave than now; a statement, however, which is fully borne out by Professor Pictet's measurements in 1822, when the depth of the glacière was less than 30 feet. Indeed, the floor had sunk considerably since my previous visit, when it was all at the same level down to the further end of the cave; whereas now, as will be seen in the section, there was a platform of stones resting on ice at that end. There are two large fissures passing into the rock, one only of which can be represented in the section, and these were full of white ice, not owing its whiteness apparently to the admixture of air in bubbles, but firm and compact, and very hard, almost like porcelain. Small stalactites hung from round fissures in the roof, formed of the same sort of ice, and broken off short, much as the end of a leaden pipe is sometimes seen to project from a wall. With this exception, there was no ice hanging from the roof, though there were abundant signs of very fine columns which had already yielded to the advancing warmth: one of these still remained, in the form of broken blocks of ice, in the neighbourhood of the open hole in the roof, immediately below which hole the stones of the floor were completely bare, and the thermometer stood at 50°. At the far end of the cave, the thermometer gave something less than 32°; a difference so remarkable, at the same horizontal level, that I am inclined to doubt the accuracy of the figures, though they were registered on the spot with due care. The uncovered hole, it must be remembered, is so large, and so completely open, that the rain falls freely on to the stones on the floor below.

By far the most striking part of this glacière is the north-west wall, which is covered with a sheet of ice 70 feet long, and 22 feet high at the highest part: in the neighbourhood of the ladders, this turns the corner of the cave, and passes up for about 9 feet under the second ladder. The general thickness of the sheet is from a foot to a foot and a half; and this is the chief source from which the fermier draws the ice, as it is much more easily quarried than the solid floor. Some of my friends went to the cave a few weeks after my visit, and found that the whole sheet had been pared off and carried away.

VERTICAL SECTIONS OF THE GLACIÈRE OF S. GEORGES.

On some parts of the wall the sheet was not completely continuous, being formed of broad and distinct cascades, connected by cross channels of ice, and uniting at their upper and lower ends, thus presenting many curious and ornamental groupings. On cutting through this ice, it was found not to lie closely on the rock, a small intermediate space being generally left, almost filled with minute limestone particles in a very wet state; and the whole cavern showed signs of more or less thaw.

It was natural to examine the structure of the ice in this glacière, after what we had observed on La Genollière. The same prismatic structure was universal in the sheet on the wall, and in the blocks which lay here and there on the floor and formed the sole remains of former columns. It was to be observed also in many parts of the ice-floor itself. The base of one large column still remained standing in its original position, and its upper end presented a tolerably accurate horizontal section of the column. The centre was composed of turbid ice, round which limpid prisms were horizontally arranged, diverging like the feathers of a fan; then came a ring of turbid ice, and then a second concentric ring of limpid prisms, diverging in the same manner as those which formed the inner ring. There were in all three or four of these concentric rings, the details showing a considerable amount of confusion and interference: the general law, however, was most evident, and has held in all the similar columns which I have since examined in other glacières. The rings were not accurately circular, but presented rather the appearance of having been formed round a roughly-fluted pillar on an elliptical base.

The examination of the ice on the wall gave some curious results. The horizontal arrangement of the prisms, which we had found to prevail in vertical columns, was here modified to suit the altered conditions of the case, and the axes of the prisms changed their inclination so as to be always perpendicular to the surface on which the ice lay, as far as could be determined by the eye. Thus, in following the many changes of inclination of the wall, the axes of the prisms stood at many different angles with the vertical, from a horizontal position where the wall chanced to be vertical, to a vertical position on the horizontal ledges of the rock. The extreme edges, too, of the ice, presented a very peculiar appearance. The general thickness, as has been said, varied from a foot to a foot and a half; and this diminished gradually along horizontal lines, till, at the edges of the sheet, where the ice ceased, it became of course nothing. The extreme edge was formed of globular or hemispherical beads of ice, like the freezing of a sweating-stone, lying so loosely on the rock that I could sweep them off in detail with one hand, and catch them with the other as they fell. Passing farther on towards the thicker parts of the ice, these beads stood up higher and higher, losing their roundness, and becoming compressed into prisms of all shapes, in very irregular imitation of the cellular tissue in plants, the axes of the prisms following the generally-observed law. There seems to be nothing in this phenomenon which cannot be accounted for by the supposition of gradual thaw of small amount being applied to a sheet of prismatic ice.