[Footnote 171: Peters, _Geologische und mineralogische Studien aus dem sudöstlichen Ungarn_, in the _Sitzungsberichte der kais. Ak. in Wien_, B. xliii., 1te Abth., S. 435. See also pages 394 and 418 of the same volume (year 1861).] [Footnote 172: Such ladders are in ordinary use in the Jura.] [Footnote 173: _Turquie d'Europe,_ i. 132 (he quotes himself as i. 180, in the _Sitzungsb, der k. Ak. in Wien_, xlix. l. 324).] [Footnote 174: L.c., p, 521.] * * * * * CHAPTER XVII. HISTORY OF THEORIES RESPECTING THE CAUSES OF SUBTERRANEAN ICE. The only glacière which is in any sense historical, is that near Besançon; and a brief account of the different theories which have been advanced in explanation of the phenomena presented by it, will include almost all that has been written on ice-caves. The first mention I have found of this cave is contained in an old history of the Franche Comté of Burgundy, published at Dôle in 1592, to which reference has been already made. Gollut, the author, speaks more than once of a _glacière_ in his topographical descriptions, and in a short account of it he states that it lay near the village of _Leugné_, which I find marked in the Delphinal Atlas very near the site of the Chartreuse of Grâce-Dieu; so that there can be no doubt that his glacière was the same with that which now exists. His theory was, that the dense covering of trees and shrubs protected the soil and the surface-water from the rays of the sun, and so the cold which was stored up in the cave was enabled to withstand the attacks of the heat of summer.[175] In the case of many of the glacières, there can be no doubt that this idea of winter cold being so preserved, by natural means, as to resist the encroachments of the hotter seasons, is the true explanation of the phenomenon of underground ice. The next account of this glacière is found in the History of the Royal Academy of Sciences (French), under the year 1686,[176] but no theory is there suggested. The writer of the account states that in his time the floor of the cave was covered with ice, and that ice hung from the roof in festoons. In winter the cave was full of thick vapours, and a stream of water ran through it. The ice had for long been less abundant than in former times, in consequence of the felling of some trees which had stood near the entrance.