he shouted down it there was a deep reverberating sound
which died away in a whisper.

Boy nature is boy nature all the world over, and Syd could not resist
the prompting which led him to drag a great piece of stone to the edge
of the crack and push it in.

He shrank back, startled at the effect of what he had done, for no
sooner had the stone disappeared than it seemed to strike on the side
and rebound, to strike again and then again and again, raising an
echoing, booming roar, which ended as suddenly as it had begun.

"I can't go down a place like that," he said, impatiently, as he shrank
away; and then he stood staring, for the noise began again. But not
below ground, for it was as if the rock had come crashing out in front
of him a hundred and fifty feet away, to be followed by a hurried
shouting; and on climbing a block of stone to his right, he made out one
of his men looking out for him, and waving his hand and shouting--"Back!
Back!"

Something was wrong. Perhaps it was an attack; and he clambered higher
so as to attract the attention of the other man, who also shouted and
waved his hand before pointing at the citadel in front.

"Something must be wrong," thought Syd, and he hurried panting on, to
get in sight of the end of the chasm at last, but he could see nothing,
only that the spars rigged up crane-fashion were not there.

He was now on the highest part of the ridge, which ran down from the
centre rock to the end; and as he clambered along he gazed seaward in
search of the frigate, but it seemed to be gone. The next moment,
though, he caught sight of her top-gallant spars, and realised that she
must be sailing right away.

The heat was tremendous as Syd struggled on, finding that he had
selected a far worse piece of the rock than had fallen to his men, and
that his task would prove hopeless without the whole party turned out to
help.

All at once, after getting over a block of rugged limestone, which
seemed full of coral, he found that he must let himself right down into
a deep crack, or else clamber to right or left, where the difficulties
were far greater, even if they were surmountable.

He paused for a few moments to wipe his streaming face, and looked up
overhead longingly at where the wind was whistling among the blocks of
stone, and then lowered himself carefully down some thirty feet, stood
listening to a curious sound which came whispering up from where the
chasm he was in contracted