Though it may be stated positively that the ice in caves is not a remnant of a glacial period, yet this cannot be done so authoritatively about subsoil ice sheets and freezing wells. At Brandon, Owego and Decorah the gravel was found frozen at the time the wells were dug, and it is of course impossible to determine for how long a time this was the case previous to the digging. The proofs, however, are so strong that the ice re-forms every winter at such freezing wells, that they may be considered as in every respect following the same general laws as glacière caves. That the ice in these wells is not the remains of a glacial period, seems proved moreover by the work of the Boston Natural History Society, which sank two wells at Brandon near to the Freezing well. One of these was only twenty-one meters distant and went through the same gravel drift. Yet it did not strike ice.[44] A somewhat similar state of things appears to be the case with the Centennial Lode and other lodes on Mount McClellan,[45] where the causes also seem to be local, as there is no ice in mines on neighboring mountains. [44] See Part IV.: Hager, page 282; Hitchcock, page 284. [45] See Part III.: Rifts of Ice, etc., page 174. _The Summer's Heat Theory._--The natives and peasants in the neighborhood of glacière caves generally believe that the ice of caves is formed in summer and melts in winter. I have met with this belief everywhere in Europe; in the Eifel, Jura, Swiss Alps, Tyrolese Alps, and Carpathians: and also occasionally in the United States. Peasants and guides tell you with absolute confidence: "The hotter the summer the more ice there is." The strange thing is that any number of writers[46]--sometimes scientific men--have accepted the ideas and statements of the peasants about the formation of ice in summer, and have tried to account for it. [46] Among them may be mentioned: Boisot, 1686; Valvasor, 1689; Behrens, 1703; Billerez, 1712; Bel, 1739; Rosenmüller and Tillesius, 1799; Sartori, 1809; Pictet, 1822; Scrope, 1826; Murchison, 1845. The belief of the peasants is founded on the fact that they scarcely ever go to any cave except when some tourist takes them with him, and, therefore, they rarely see one in winter, and their faith is not based on observation. It is, however, founded on an appearance of truth: and that is on the fact that the temperatures of glacière caves, like that of other caves or that of cellars, are colder in summer than the outside air, and warmer in winter than the outside air. Possessing neither reasoning powers nor thermometers, the peasants simply go a step further and say that glacière caves are cold in summer and hot in winter.