, at all events, and a very swift one, too,
for the rocky walls on either side were almost close enough to touch
with the paddles, and they were moving at a dizzy rate of speed.

"There are rapids below us," said Forbes. "I can hear them dimly."

Melton's hearing was unusually acute, for as yet the rest could hear
nothing, but in a few seconds the distant roar was audible to all, and
it grew ominously louder with every second.

They grasped the sides of the canoe in anxious suspense--for it was
useless to paddle--and the angry waters were almost in sight, when Sir
Arthur dropped his torch, and instantly they were plunged in total
darkness.

No time remained to strike a fresh light. The sullen crash of the waters
drowned the sound of their voices, and the canoe blindly took its own
course and they felt the chill spray spattering their faces.

"Bump, bump, bump," went the quivering boat, grinding and crashing on
loose rocks, and then with one terrific lurch, that sent them sprawling
on their knees, the violent tossing subsided and the choppy waves
smacked the bottom of the canoe.

With some difficulty Guy lit a fresh torch, and its light revealed a
strange condition of things.

No shore was visible on either side, and overhead was empty space
instead of the low lying roof that always met their gaze.

"We are no longer moving," cried the colonel in astonishment.

"Impossible!" exclaimed Guy, but on putting his hand in the water all
doubt was instantly removed. The canoe was stationary.

They paddled on to the right, to the left, in every direction, but the
dark water lay calm and sluggish on all sides.

"We are on a lake," said Guy. "There is no doubt of it; a vast
underground lake."

"There must be an outlet on the other side, though," replied Melton.
"All we need do is to paddle across and find it."

"But which is the proper side?" said Canaris. "Are we headed straight
now?"

"By Jove, I don't believe we are," replied Guy. "I'm afraid we are
completely mixed up. We will paddle until we reach the shore, and then
follow it till we come to the outlet."

"Yes, that will do very well," said the colonel. "The lake cannot be so
very large. I wish we had time to complete a survey of it. I should like
to make a report to the Royal Geographical Society."

"I wish the honorable members of the R. G. S. could change places with
us," said Sir Arthur, with a groan. "I have no doubt some of those
lunatics would enjoy