on, or they'll see the reflection of the light."

"Can't," whispered back Mike faintly. "I've got my boot down a crack,
wedged in."

Vince seized him sharply by the shoulder, and Mike nearly fell back into
the water; but this acted like a lever, and the boot was wrenched free,
just as another whistle was heard and its answer, both sounding
strangely near.

Quite certain that if they did not get in farther the reflection from
the lanthorn must be seen, Vince waded on, with the water rising from
his knees to his thighs, and then, feeling terribly cold, nearly to his
waist.

"We mustn't go any farther," said Mike in an excited whisper, "or we
shall have to swim."

"Very well, then, we must swim," said Vince, holding the light well up
above the water, and looking anxiously along the dark channel ahead, the
roof not being two feet above their caps.

Deeper still--the water above their waists--but the cavern went nearly
straight on, and Vince was about to open the door and blow out the
light, when Mike caught his arm.

"Don't do that," he whispered: "it would be horrible here, with those
beasts about. There, you can hear one swimming, and we don't know what
else there may be."

"But they'll see the light."

"Well, let them," said Mike desperately. "I'd rather wade out."

"I'll risk it, then," said Vince; and then he drew a breath of relief,
for at the end of a couple of yards the depression along which they had
passed was changing to a gradual rise of the cavern floor, and the water
fell lower and lower, till it was considerably below their waists, and
soon after shallow in the extreme.

They went on with mingled feelings, satisfied that they were getting
where they would not be discovered, and also into shallow water, that
promised soon to rise to dry land; but, on the other hand, they kept
having hints that they were driving back living creatures, which made
known their presence by wallowing splashes, that echoed strangely along
the roof, and made the boys grasp club and cudgel with desperate energy.

To their great joy, now, on looking back they found that they could not
see the daylight shining in from the mouth upon the water, and as, in
consequence, any one gazing into the cave was not likely to see the dim
rays of their lanthorn, the boys paused knee-deep, glad to find that
they need go no farther along the narrow channel--one formed, no doubt,
by the gradual washing away of some vein of soft felspar