noise.

"What's that?" asked the professor.

"Sounded like some beast roaring," answered Jack.

"Look out!" shouted Andy, springing back, and bringing his gun to bear.
"We're in for it now!"

"Sea lions, by their looks!" exclaimed the inventor. "A whole crowd of
them and they are right between us and the ship!"

The next instant the party came into full view of the beasts. There were
about two hundred of them, great big brutes, with sharp tusks. At the
sight of the men and boys the animals set up a chorus of roars that
sounded as if several score of real African jungle lions had broken
loose. At the same time the beasts, with curious hitchings of their
unwieldly bodies, advanced on the adventurers!

"Get your guns ready," cried Andy. "These fellows mean business! Make
every shot tell!"

He had already begun firing and two of the sea lions toppled over in
quick succession, testifying to his good aim. Then the boys, the two
helpers, the professor and Washington began a fusillade that made the
icy regions echo and re-echo as though a battle was in progress.

But the number killed among them, and the sound of the guns, did not
halt the progress of the beasts. On and on they came, their roars
increasing in fierceness.

The continuous firing could not be kept up long. Already the old
hunter's gun was empty, and there was no spare ammunition now. One after
another the rifles of the others were emptied of their cartridges. Still
the beasts came on.

"We must retreat!" shouted Andy. "Back to the ice cave! They can not get
us there!"

"But what about the airship! We must regain that at any cost!" called
the professor.

"Wait until these beasts go away!" yelled Andy. "If they get us down
it's only a matter of seconds before they'll kill us with those tusks!
Run back!"

All turned to execute this command. There was only a narrow opening in
the slowly encircling ring of sea lions, and this the adventurers made
for, running toward the ice cave. They had passed beyond the mass of the
beasts, when a loud cry from Jack startled them. At the same time he
pointed ahead.

There, coming on at full speed was a pack of polar bears! The
adventurers were between the two forces of enraged animals!

CHAPTER XII

A MYSTERIOUS MESSAGE

"It's all up with us now!" shouted Andy. "I wish I had never come to the
north pole!"

"How shall we escape?" yelled the professor.

Not knowing what to do, the whole party stood s