"How did you gain the rock, Frank?" asked Harry.

"When I saw you swept off the tree trunk I slipped off too," replied
Frank, "and when I felt myself dragged into the pool I struck out
for the rock. I confess, though, I didn't have much hope of
reaching it till I was slammed into it with a blow that almost
cracked my ribs and knocked all the wind out of me. I managed
however to grab hold of a depression in the surface and maintain my
grip on it. I had hardly dragged myself up when you were hurled
against it. I thought I had lost you, for the water pulled like a
draught-horse, but I managed to hold on to you and here we are."

"And a worse position we could not possibly be in," added Harry.

"Unless we were in there," retorted Frank pointing, not without a
shudder, to the whirling open mouth of the pool which had sucked
down the wreck of their canoe.

"What is it do you suppose?" asked Harry wonderingly.

"The mouth of a subterranean river I guess," replied Frank. "I have
read of such things."

"But why didn't Desplaines warn us of our danger," said Harry
bitterly, "if we ever get out of this I shall tell him my opinion of
him pretty strongly. We might have been killed and we may yet."

"He did warn us," replied Frank calmly.