Pallas describes many caves in various parts of Russia, but never seems to hint at the existence of ice in them, though he specially mentions their extreme cold. Some of these occurred in gypsum, and some in limestone; and the gypseous caves showed universally a very low temperature, though still far above the freezing-point.[116] Thus in the dark cavern of Barnoukova,[117] on the Piana, in a rock of gypsum, while the thermometer in the shade stood at 75°.2, the temperatures at various points in the cave were,--at the entrance 59°.36, 25 feet from the entrance 46°.4, and in the coldest part 42°.8. This cold he describes as insupportable. The temperature of the water which had accumulated in the coldest parts of the cave was 48°.8, considerably higher than the surrounding atmosphere; from which Pallas concluded that the cold of gypsum-caves is due to the acid vapours which are generally observed in grottoes of this description. In May 1770, he found snow on the sloping entrance to the cavern of Loeklé, in the neighbourhood of the Oufa; but the air of the interior was not colder than was to be expected in a deep cave. Sir R. Murchison wrote to Russia for further information with respect to this cave in January 1865, and again in the beginning of April, addressing his second enquiry to the Secretary of the Imperial Academy. In reply, the Secretary says that he is not aware that any thermometric observations have been made in the cavern. He encloses a short statement by M. Helmersen, one of the members of the Academy, to the following effect:--About 50 versts SE. of Miask, in the chain of the Ural, is a copper mine, called Kirobinskoy, which was abandoned more than fifty years ago. On the 7th July, 1826, M. Helmersen found a thick wainscoting of ice on the sides and roof and floor of the horizontal gallery, within 10 feet of the entrance. He was assured that this ice never melts, and that its thickness is greater in summer than in winter. M. Helmersen adds, that to the best of his belief no one has investigated the cavern of Illetzkaya Zastchita since Sir R. Murchison's visit. _The Ice-Cavern of the Peak of Teneriffe_.[118] This cave is at a height of 11,040 feet above the sea, and is therefore not far below the snow-line of the latitudes of the Canary Isles. The entrance is by a hole 3 or 4 feet square, in the roof of the cave, which may be about 20 feet from the floor. The peasants who convey snow and ice from the cave to the lower regions, enter by means of knotted ropes; but Professor Smyth had caused his ship's carpenter to prepare a stout ladder, by which photographic instruments and a lady were taken down.