Glacières are, in general, at fairly high altitudes. The Schafloch is at 1780 meters; Skerisora in Transylvania at 1127 meters; Dóbsina at 1100 meters; the Glacière de Saint-Georges at 1208 meters. It is true that there is one freezing cavern in the sub-tropical latitude of Teneriffe, La Cueva de la Nieve; but it is at an altitude of 3300 meters, and where snow falls every year in the open on the Peak. Unless some freezing cave is hereafter discovered in a region where there is no ice in the open in winter, I do not see how the imperative necessity of the cold air of winter for forming the supply of ice can be controverted. _Thermometric Observations._--That the cold air of winter is the important factor in the production of cold is proved, also, by the thermometric observations recorded in various caves by different observers. They all tell the same tale: that the temperatures vary with those of the outside air, that they are lowest in winter and highest in summer. I quote in the "List of Glacières"[57] a few of those published; but there are many more, and they all show the same general characteristics. [57] See Part III.: Decorah, page 178; Chaux-les-Passavant, pages 203-5; La Poujade, page 208; Montarquis, page 218; Saint-Georges, page 219; Schafloch, page 223; Kolowratshöhle, page 227; Schellenberger Eisgrotte, page 228; Frain, page 252; Dóbsina, page 253; etc. A comparison of all the figures recorded proves that, as a rule--inside of glacière caves--from about the first of November to the first of July, there are winter temperatures, that is temperatures below freezing point; and from about the first of July to the first of November, there are summer temperatures, that is temperatures above freezing point.