crystals of the most wonderful form.

Before him, at the distance of a dozen feet, he could dimly make out the
figure of the major, while behind stood the group formed by their
companions, looking like so many silhouettes in black against the pale
light sent down the chasm from above.

"Mind what you're doing," said the captain. "Don't go in too far."

"All right!" cried the major; "there's good bottom. It's a lovely
sulphur cave. Coming in?"

"No," said the captain, sitting down; "I'll wait for you. Make haste,
and then we'll go back another way."

"Can you see the sides, Mark?" said the major.

"Yes, sir. Lovely!" replied the lad. "I should like to take a
basketful. I'll break a piece or two off."

"Wait a bit," said the major; "there is a lovely piece here. What's
that?"

Mark listened, as he stood close to the major, where the cavern went
right in like a narrow triangle with curved sides.

A low hissing noise saluted their ears, apparently coming from a great
distance off.

"Snakes!" whispered Mark.

"Steam!" said the major. "Why, Mark, this passage must lead right into
the centre of the mountain. There, listen again! You can hear a dull
rumbling sound."

"Yes, I can hear it," said Mark in an awe-stricken whisper.

"I dare say if we went on we should see some strange sights."

"Without lights?" said the captain, who had approached them silently.

"Perhaps we should get subterranean fire to show us the interior of the
mountain. What do you say?--shall we explore a little further? One
does not get a chance like this every day."

"I'm willing to come another time with lights, but it would be madness
to go on in the dark. How do you know how soon you might step into some
terrible chasm?"

"Without the slightest chance of being shot out again, like Billy
Widgeon!" said the major. "You are quite right; it would be a terribly
risky proceeding."

They listened, and this time there came a low boom and a roar as if
there had been an explosion somewhere in the mountain, and the roar was
the reverberation of the noise as it ran through endless passages and
rocky ways echoing out to the light of day.

"No, it does not sound tempting," said the major. "I don't want to go
far. But I must get a specimen or two of this sulphur for the ladies to
see."

He walked on cautiously.

"Mind!" said the captain.

"Oh, yes, I'll take care," came back out of the darkness. "I can see my
way yet, a