The peasants report that there
is always ice in summer, and never in winter, when the sheep retreat to
the cave on account of its warmth. Steininger[149] found a thickness of
3 feet of ice on September 19, 1818, but it was evidently in a melting
state, and the thermometer stood at 36.5 F. in the cavern. He describes
it as possessing a narrow entrance facing north, entirely sheltered from
the sun by lava-rocks, and by the trees of a wood which covers the cone
of scoria.
Scrope believes that this is the mouth of one of the arched galleries so
frequently met with under lava in Iceland, Bourbon, and elsewhere; and
on this he founds his explanation of the phenomenon. If the other
extremity is connected with the external air at a much lower level, a
current of air must be constantly driven up this gallery, and in its
passage will be dried by the absorbent nature of the rock--which is
perhaps partly owing to the sulphuric or muriatic acid it
contains[150]--and the evaporation caused by this current produces a
coating of ice on the floor of the grotto, where there is a superficial
rill of water.
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