lf, if he could pass through
once unprepared and taken by surprise, he could certainly reverse the
action.

In this spirit, and so as to get a little encouragement and inspiriting
for another task--in other words, so as to enjoy the feeling that a way
of retreat was open to him--he walked back toward the depression along
which the vapour rose, examining every step of the way, and noticing
that by degrees all growth ceased as he approached, and that the ground
gradually grew softer and then spongy to the tread, as if he were
walking over a bog.

The air remained very clear and good to breathe as he went on nearer and
nearer, seeing now that the fumes rose softly all along one jagged line
such as might have been formed by the earth opening right before him.
But there was no opening. As far as he could penetrate the dim mist,
the earth looked perfectly level, but the vapour rose from it as it does
or appears to do from a swampy meadow on a fine autumn evening; and it
was evident to him that he might try and dash through without fear of
running headlong into some chasm.

Just then, as he stood gazing down at the bottom of the curtain, the
idea struck him that perhaps there had been a wide rift right across to
right and left; that it had been filled up by volcanic matter, and the
vapour was caused by this lava or hot liquid mud slowly cooling down.

Convinced that this must be so, he had full endorsement of the
correctness of his theory, for on lifting one foot to go on, he found
that the other was sinking slowly, and a little further investigation
showed him that a faint thread of vapour was rising from the spot where
his heel had been.

The meaning of this barren space, and the reason for the earth feeling
spongy, was plain enough now, and he knew that he was walking over so
much half-fluid volcanic pitch, whose surface was slightly hardened and
formed the elastic springy band.

If it gave way!

The thought was enough to make the stoutest shudder, and feeling now
that his safety lay in movement, he took a few more steps towards the
vapour, finding himself, before he was aware of the fact, and without
the slightest mistiness being visible, within its influence.

He started away in alarm, for he was suffering from a slight attack of
vertigo, which did not pass off for a minute or two, and he walked, or
rather staggered, back, with the tough elastic film over which he walked
now rising and falling with an undulator