though in appearance resembling the rest of
of the lava, yet was not sufficiently thick or
strong to bear the human weight.
That the floors or bottoms of these cavities
owe their colored appearance to the
different kinds of sulphur, iron, and other
metallic substances which have melted and
dropped from the arched surface, will readily
be perceived, without the necessity of my
remarking i t ; and it will likewise easily be
understood, that the spiculae, which hang
from the ceilings, are nothing more than a
part of the lava, more or less intermixed
with strong substances, which, whilst dropping,
had cooled and become indurated.
§ XXVIII.
It has already been mentioned, (§ xvii;)
Attempts with th e that the great heat arising
boring-instruments. o .1 , ® trom the lava was no small
obstruction to the experiments we had hoped
to have made with our boring-instruments,
in the hilly country, as well as in the vallies;
insomuch, that I began to entertain fears
lest this circumstance should render these
instruments quite useless ; preventing us, as
it did, from employing them, except where
the ground was proportionably cool. It is
scarcely in the power of any one to form
an idea of the difficulty that attended this
part of our labors. To be continually turning
the instruments round, and working
through the hot, hard, and uneven lava,
while we were at the same time treading
upon its sharp-pointed edges, was certainly
a task as painful as it was irksome. Nevertheless,
by these trials, I found that the lava
in some places did not lie more than six or
eight feet deep; that in many it did not exceed
ten feet; and that wheresoever, as was
the case in certain situations, it was far
deeper, its depth seemed wholly to depend
on the peculiar nature of the country.
Both below the lava, and close by its side,
was found either sand or earth of the same
kind as that which appears every where in
this district, at a distance from the fire, as
in the peat-bogs or in the grounds where
the sea-lyme grass (Elymus arenarius)
grows; but no kind of slate could be discovered
in the neighborhood. The boring-
instruments were useful, in enabling me to
ascertain the quality of the soil below and