It is evident that the current which passes up into the fissure in winter, is favourable to the introduction of the colder air from without; while the opposite current in summer keeps up a supply of cold air in the cave, and so increases its powers of resisting the attempts of the heated external air to make a partial entrance.

Both these currents, then, favour the glacial conditions of the cave, and to some extent counterbalance the disadvantages of its situation: viz., its aspect, towards the south-east; the large size of its opening to the air, and the absence of all shelter near the mouth, such as is so often provided by trees or rocks.

The small depth of the cave, scarcely amounting to 18 feet below the level of the entrance, is also a great disadvantage.
The people of Pralong asked, on the return of the party, what had been found in the _grand' cave_, and the answer reduced them to silence for a few moments.

Their prejudices, however, were invincible, and they persisted in their belief that a true glaciere ought to have no ice in it in the winter.

M.Thury did not enquire from what source they drew their ideas of a true glaciere.
There is a book, in three volumes, on the 'Glacieres of the Alps,' by M.
Bourrit, dedicated to Buffon, in which is a description of the Valley of Reposoir; but no mention whatever is made of the _grand' cave_.