out!" he cried, loudly, and, raising his piece, he fired at the
great leopard-like creature which had evidently taken refuge here, and
now bounded out with a fierce growl, and away along the rocks by the
edge of the lake.

The bullet sent after it evidently grazed the animal, for it sprang into
the air and fell with a tremendous splash into the water, but scrambled
out again, and went bounding away, while, instead of following their
comrade's example, Oliver and Drew stood listening, appalled by the deep
roar as of subterranean thunder, which ran away from close to their feet
to die away in the distance, and then rise again--a strange
reverberation that seemed to make the rocks quiver upon which they
stood.

"We must have him some day," said Panton, stepping right down on a
stone, whose surface was just above the level of the water; and now, for
the first time, Oliver saw that there was a slightly perceptible current
running on either side of this stone, the water gliding by with a glassy
motion, this evidently being the outlet of the lake; and on joining
Panton he found himself facing what resembled a rugged Gothic archway at
the foot of the stony walls, where a couple of great fragments of lava
had fallen together.

"Why, it is a cavern!" cried Oliver, as he bent forward, and tried to
peer into the darkness before him.

"A cavern? Yes; Aladdin's cave, and we're going to explore it," cried
Panton. "Now then, Smith, five candles, please, and all lit ready for
us to go in and see what there is to be seen."

Smith walked right in, stepping from stone to stone for a few yards, and
then leaping off the block on which he stood in midstream to the lava at
the side; and, upon Oliver following him, he found that he was standing
upon another stream, one which had become solid as it cooled, while the
water which now filled the cup-like hollow had gradually eaten itself a
channel in the stone, about a quarter of the width of the lava, and this
flowed on into the darkness right ahead.

"What do you think of it?" cried Panton.

"Wet, dark, and creepy," said Oliver, as he listened to a peculiar
whispering noise made by the water as it glided along in its stone
canal, the sound being repeated in a faint murmur from the sides and
top.

Then _scritch-scratch_ and a flash of light which sank and then rose
again, as the splint of wood, whose end Smith had struck, began to burn
strongly.

"Now, Billy! Candleses!" cried the