[Footnote 178:  Tournefort (Voyage du Levant, iii. 17) believed that the ammoniac salt, of which the earth was full in some districts near Erzeroum, had something to do with the persistence of snow on the ground there.]

[Footnote 179:  Hist, de l’Acad., an 1726, p. 16.]

[Footnote 180:  But see on this point the experience of M. Thury, in the Glaciere of S. Georges (Appendix).]

[Footnote 181:  Sir Roderick Murchison’s suggestion of the possible influence of salt in producing the phenomena of his ice-cave in Russia, did not, of course, proceed upon the supposition of salt actually mingling with water, but only of its increasing the evaporation of the air which came in contact with it.]

[Footnote 182:  Mem. presentes a l’Academie par divers Scavans, i, 195.]

[Footnote 183:  A long account was published in a history of Burgundy, printed at Dijon, in quarto, in 1737, which I have not been able to find.  It was from the same source as the account in the Hist. of the Academy, in 1726.]

[Footnote 184:  I took this earth to be a collection of the particles carried down the slope of ice by the heavy rains of the month preceding my visit.  M. de Cossigny speaks of the abundant rains of July, his visit being in August.]

[Footnote 185:  Recherches sur la Chaleur; Geneva and Paris, 1792.]

[Footnote 186:  P. 65.  Now called Annales des Mines.]

[Footnote 187:  T. xlv. p. 160.]

[Footnote 188:  Bibliotheque Universelle de Geneve, Premiere Serie, t. xx.]

[Footnote 189:  See De Saussure’s account of his numerous observations of such caves in the Voyage dans les Alpes, sections 1404-1415.]

[Footnote 190:  P. 271.]

[Footnote 191:  P. 271.]

[Footnote 192:  xxi. 113.]

[Footnote 193:  P. 271.]

[Footnote 194:  Daubuisson estimated the depth in question at from 46 to 61 feet, while Kupffer put it at 77 feet.]

[Footnote 195:  De Saussure found a variation of 2 deg..25 F. at a depth of 29.5 feet; but this was in a well, where the influence of the atmosphere was allowed to have effect.  Naturally, the fissures which there may be in the rock surrounding a cave will increase the annual variation of temperature, by affording means of easier penetration to the heat and cold.

Sir K. Murchison’s cavern in Russia would seem to be entirely sui generis.]

* * * * *

CHAPTER XVIII.

ON THE PRISMATIC STRUCTURE OF THE ICE IN GLACIERES.