. Look at that piece lying there; only
that it's of a beautiful silvery grey, it looks just like one of the
pieces of cinder which pop out of the fire."

"Want a pretty good-sized fire for a piece like that to pop out of,
sir," said the man scornfully.

"Well, it must have been a good-sized fire when this great mountain was
in eruption, and the red-hot lava boiling over the sides of the crater
and running down."

"But do you really think it ever did, sir?"

"I have no doubt about it whatever. Look at that piece lying half
buried in the black sand. What is that?"

"Looks like black glass, sir," said Ned, kicking a piece of obsidian.

"Well, it is volcanic glass. How could that have been made without
heat?"

"I dunno, sir. It caps me."

"You said the place was hot."

"No need to say it, sir. I'm as hot as hot. Brings me out in a
prespiration."

"St! don't talk so loudly, Ned. The place echoes so."

At that moment the man laid his hand upon Jack's arm and pointed
downward.

The lad followed the direction of the pointing hand, to see that a group
of the blacks were coming in their direction, and for the moment Jack
felt that they must be seen, until he saw that they were standing well
in the shadow.

His first impulse was to catch Ned's arm, stoop down and hurry away to
reach the shelter of the trees, but Ned stopped him.

"No good, sir. We should be seen. Let's go right in here."

"What, to be trapped?"

"They mightn't come in here, sir, and if they did, perhaps they couldn't
find us. Anyhow they're sure to see us and come after us if we go
outside."

The wisdom of the words was evident enough, and with a sigh Jack drew
back with his companion, startling some birds from a shelf where they
seemed to be nesting within reach of his hand, and sending them rushing
out uttering their alarm notes.

"Are we in far enough, Mr Jack?" said Ned.

"No: any one could see us here. Come along."

They went on inward for another twenty yards, the mouth of the entrance
still being in full view. It was awkward travelling, the black sand
having given place to loose pieces of scoria and obsidian, some pieces
of which crackled under their boots, and took revenge by entering into
the soles. As they went in the place widened out, but remained much
about the same height overhead, the highest portions of the roof being
nearly within touch of Ned's hand.

Here the latter stopped again.

"Don't let's go any