This sand
is a non-conductor of heat, and would therefore tend to preserve the
snow from complete fusion when the hot lava-stream passed over it, and
thus the existence of the underground glacier may be explained. The
peasants of the district are so well acquainted with the non-conducting
properties of volcanic sand, that they secure an annual store of snow,
for providing water in summer, by strewing a layer of sand a few inches
thick upon a field of snow, thus effectually shutting out the heat of
the sun. It is curious that when De Saussure visited Chamouni for the
first time, his attention was arrested by the sight of women sowing what
seemed to be grain of some kind in the snow; but, on enquiring, he found
that it was only black earth, which the inhabitants spread on the snow
in spring, in order to make it disappear sooner. He was told that snow
thus treated would melt a fortnight or three weeks before the ordinary
time for its disappearance in the valley; but it will be seen that this
does not contradict the theory of the Sicilian peasants.
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