king, that the supposed independence of several orifices of
eruption in one crater like Kilauea, when adduced in confirmation of the
doctrine of two distinct sources of volcanic action underneath one
mountain, proves too much. No one can doubt, that the pools of lava in
Kilauea have been derived from some common reservoir, and have resulted
from a combination of causes commonly called volcanic, which are at work
in the interior at some unknown distance below. These causes have given
rise in Mount Loa to eruptions from many points, but principally from
one centre, so that a vast dome of ejected matter has been piled up. The
subsidiary crater has evidently never given much relief to the
imprisoned, heated, and liquefied matter, for Kilauea does not form a
lateral protuberance interfering with the general shape or uniform
outline of Mount Loa.

_Geysers of Iceland._--As aqueous vapor constitutes the most abundant of
the aeriform products of volcanoes in eruption, it may be well to
consider attentively a case in which steam is exclusively the moving
power--that of the Geysers of Iceland. These intermittent hot springs
occur in a district situated in the southwestern division of Iceland,
where nearly one hundred of them are said to break out within a circle
of two miles. That the water is of atmospheric origin, derived from rain
and melted snow, is proved, says Professor Bunsen, by the nitrogen which
rises from them either pure or mixed with other gases. The springs rise
through a thick current of lava, which may perhaps have flowed from
Mount Hecla, the summit of that volcano being seen from the spot at the
distance of more than thirty miles. In this district the rushing of
water is sometimes heard in chasms beneath the surface; for here, as on
Etna, rivers flow in subterranean channels through the porous and
cavernous lavas. It has more than once happened, after earthquakes, that
some of the boiling fountains have increased or diminished in violence
and volume, or entirely ceased, or that new ones have made their
appearance--changes which may be explained by the opening of new rents
and the closing of pre-existing fissures.

Few of the Geysers play longer than five or six minutes at a time,
although sometimes half an hour. The intervals between their eruptions
are for the most part very irregular. The Great Geyser rises out of a
spacious basin at the summit of a circular mound composed of siliceous
incrustations deposited