termined to go as far forward
as the smoke would permit. The prospect was gloomy enough; but the
situation of Bob nerved them all to the effort. Besides, they were
encouraged by the fact that the smoke would sometimes retreat far
up, exposing the surface to the very crest of the crater. So they
advanced, clambering over the rough blocks, and drew nearer and
nearer to the summit. At length a heavy mass of black smoke came
rolling down. It touched them. It enveloped them. It folded itself
over them and under them. Each one fell flat on his face at Michael
Angelo's warning, and covered his mouth and nostrils with his
handkerchief, so as to keep out the sulphurous vapors. It was almost
suffocating; breathing was difficult and painful, and it seemed a
long time before the blackness of the darkness was mitigated. But
at last the smoke withdrew itself, and the whole party stood up,
and looked around painfully for one another, panting heavily, and
drawing laborious breaths.

"You can't go any further," said Uncle Moses. "I ain't goin to
let you resk your lives, boys. You must all go back, an I'll go
for'ard."

"No, uncle; I'll go," cried Frank.

"And I," cried David.

"And I," cried Clive.

"None of you shall go," said Uncle Moses, firmly. "I tell you I'm
goin. I order you to stay here, or go back." Uncle Moses was deeply
agitated, and spoke with unaccustomed sternness. "Go back," he
said; "I'll find Bob, or leave myself there. Go back. D'ye hear?"

He darted forward, and turned to wave his hand at the boys. But
Frank had already sprung upward, swiftly and eagerly. Onward he
went, going first to the left and then to the right. David and
Clive also rushed forward. Uncle Moses toiled after them, calling
on them to come back. Michael Angelo followed slowly, looking on
with a face of fearful apprehension.

Frank was far ahead. He had come to a place where the lava blocks
ended, and the soil was sandy. Here he paused for an instant, and
took a swift glance around. He started. He had seen something. He
made a quick gesture and then sprang away to the right.

All this had not taken many minutes. It was an act of desperation
on the part of Frank, but he was determined to save Bob or perish.
Fortunately the smoke did not descend just at that moment, but was
floating up from the summit, so that the edge of the crater could
be seen, with a dull yellow gleam, caused by the sulphur that lay
mingled with the sand.

Frank had se