complete protection. It is this elastic cushion of vapour which
imparts that feeling of softness described by M. Houdin; for it is
with it alone that the hand comes into contact.

[1. Houdin's Autobiography, ii 270]

Geysers have been recently discovered in California; but the jets
do not rise higher than twenty or thirty feet. They are, however,
very numerous, there being upwards of a hundred openings within a
space of half a mile square. The vapour from the whole group rises
to upwards of a hundred and fifty feet into the air. The boiling
water issues from conical mounds, with great noise. The whole
ground around them is a mere crust, and when it is penetrated the
boiling water is seen underneath. The Californian geysers, however,
are impregnated, not with silica, like those of Iceland, but with
sulphur, of which they form large deposits. The sulphurous vapours
from the water corrode the rocks near the fountains; nevertheless
trees grow, without injury to their health, at a distance from them
of not more than fifty feet.

Besides obsidian, already mentioned as a product of its volcanoes,
Iceland is famed for another mineral of great scientific value. It
is that fine variety of carbonate of lime named Iceland-spar.
Transparent and colourless, like glass, this mineral possesses the
property of double refraction--any small object viewed through it
in a particular direction appearing double. It is much used for
optical purposes--especially for obtaining polarized light.

There is another volcano lying far to the northward of Iceland. It
is in the island of Jan Mayen, off the coast of Greenland, and has