and till they had eaten lunch. Zeb
sliced off some venison cutlets and cooked them to a turn over hot
wood coals. The boys thought they had never tasted anything better
than the fresh meat.

While the plates and knives and forks were being washed and put away,
the professor wandered off on his perennial quest of rocks and
specimens. He said that he would be back in a short time but was
anxious not to miss the opportunity of finding some possibly rare
stones.

But everything was ready and the boys were waiting impatiently half an
hour later, and there was no sign of the professor.

Suddenly they heard his voice shouting to them from the distance.

"What's he saying?" asked Jack.

"Hark!" admonished Tom.

The professor's shouts came plainly to their ears the next minute,
borne on a puff of wind that swept through the canyon.

"Help! Help!" was the burden of his cries. "Get me out!"

"Now, what's happened to him?" demanded Zeb, with a trace of
impatience.

"I don't know, but he must be in trouble of some sort," cried Jack.

"Maybe it's another donkey," mischievously suggested Dick.

The cries were redoubled. They waited no longer but started off across
the island on the run. Zeb carried his big forty-four revolver.

CHAPTER XXIX.

A MUD BATH.

The ground was rough and rocky but they made good time. Bursting
through a screen of trees from beyond which came the professor's
piteous cries, they received a shock.

The man of science was in the center of a large, round hole full of
black mud that bubbled and boiled and steamed as if it were alive. All
that was visible of the professor was the upper part of his body.

Seriously alarmed, the boys shouted to him to keep up his courage, and
that they would get him out.

"How did you get in?" asked Zeb, cupping his hands.

"I fell in," rejoined the poor professor. "The ground gave way under
my feet. Hurry and get me out, it's terribly hot."

They looked about them desperately for some means of extricating him
from his predicament. But just at the moment none was offered, and
with every struggle the professor was sinking deeper in the black,
evil-smelling pool of mud.

"Gracious, what are we to do?" cried Jack in despair.

"He's too far out to reach him," said Zeb, equally at a loss.

"But we must do something," chimed in Tom.

Suddenly Zeb had an inspiration. A tree grew on the banks of the mud
volcano, the sudden caving in of which, under the pr