A third visit, in January 1835, gave no results; but on January 21, 1838, the Professor succeeded in determining some very remarkable facts. A depression in the sloping plain is called, _par excellence_, the ice-hole; and this is surrounded by firs and birches, which grow within three or four fathoms of the edge of the hole, so that the rays of the sun do not reach the hole in winter. Fresh snow lay on these trees; and there was nowhere any sign of melted snow, or of the formation of icicles. The basaltic _débris_, in which ice had been found in the summer, covers here a space of 5 fathoms long by 3 or 4 broad, immediately at the foot of a steep basaltic precipice. At eleven in the morning the temperature was 14° F. in the shade; and snow lay all round the ice-hole, to a thickness of 1-1/2 or 2 feet. The snow which covered the _débris_ was pierced by holes, which could not have been caused by the sun, for its rays did not penetrate the trees; and, indeed, no sun had been visible for some days. These holes were generally turned towards the north, and were like chimneys. On investigation, it was found that icicles hung down into them, showing, of course, past or present thaw, and within the cavities no ice was found. The thermometer gave here from 27°·5 F. to 25°·15 F.; but in the crevices, into which the thermometer could not be pushed, the hand discovered a warm air. The moss drawn from these crevices was found to be steeped in unfrozen water, and it froze promptly when brought into the outer air. The party afterwards climbed up the precipitous basalt, and reached, at 3 P.M., a level covered with large blocks of the same material, where the thermometer was slightly under 12° F. in the shade. The blocks were for the most part stripped of snow, and in some cases thin shields of ice were observed standing out two or three inches from them, forming hollow chambers, in which an agreeable warmth was found. These shields were invariably on the south side of the stones, the north side being free from ice and snow alike. In some places vapours were seen to rise. The thermometer gave 41° F. at a depth of six inches among the stones, though the external temperature, as has been said, was 12° F. For eight days previously, the thermometer had been always far below the freezing point, and on the 17th (four days before) had been 13° below zero (F.). On the 19th and 20th heavy snow had fallen. All these facts seem to show that the warmth which had caused the chimneys in the snow over the ice-holes, and the heated vapours on the higher parts of the mountains, proceeded from within, and not from without.