years, becoming gradually more inclosed by the subsequent eruptions.
At one point where this compact snow--which has, indeed, taken on the
form of ice--has been revealed to view, it has been quarried and
conveyed to the towns upon the seacoast. It is likely that there are
many such masses of ice inclosed between the ash layers in the upper
part of the mountain, where, owing to the height, the climate is very
cold. This curious fact shows how perfect a non-conductor the ash beds
of a volcano are to protect the frozen water from the heat of the
rocks about the crater.

The furious rains which beset the mountain in times of great eruptions
excavate deep channels on its sides. The lava outbreaks which attend
almost every eruption, and which descend from the base of the cinder
cone at the height of from five to eight thousand feet above the sea,
naturally find their way into these channels, where they course in the
manner of rivers until the lower and less valleyed section of the cone
is reached.

Such a lava flow naturally begins to freeze on the surface, the lava
at first becoming viscid, much in the manner of cream on the surface
of milk. Urged along by the more fluid lava underneath, this viscid
coating takes a ropy or corrugated form. As the freezing goes deeper,
a firm stone roof may be formed across the gorge, which, when the
current of lava ceases to flow from the crater, permits the lower part
of the stream to drain away, leaving a long cavern or scries of caves
extending far up the cone. The nature of this action is exactly
comparable to that which we may observe when on a frosty morning after
rain we may find the empty channels which were occupied by rills of
water roofed over with ice; the ice roofs are temporary, while those
of lava may endure for ages. Some of these lava-stream caves have been