It was very evident that they could not hold put indefinitely in
this position.

Their attention was attracted as they clung to their water-swept
tree-trunk by a dark object whirling about in the boiling pool. It
was swept dizzily round and round in ever decreasing circles toward
the middle of the fatal vortex. Suddenly it shot downward out of
sight, but as it did so Frank had seen something that kindled one
ray of hope--though a feeble one. Before the canoe had taken the
fatal downward plunge it had hesitated for a minute as though caught
on something; and then the boy leader saw for the first time that in
the center of the pool there was a rock, although the water that
submerged it to the depth of an inch or so prevented its being seen
at first glance.

Frank turned to Harry and told him of his discovery.

"If we are cast into the pool let us make up our minds to get to
that rock. Keep your mind concentrated on it. Don't let the idea
leave you for a second and perhaps--I say 'perhaps'--we can make
it."

Harry shook his head despairingly.

"I can hardly keep my grip on this tree. I don't believe that I
could possibly manage to swim even a few yards," he groaned.

"You must," said Frank sharply. "Don't give in now, Harry. Stick
it out."