the
recital of how the white thing had suddenly disappeared, Washington
refused to continue his watch, unless some one stayed with him.

Mark volunteered to do this. He was anxious to see if the ghost would
reappear to him. But nothing happened; and the rest of the night passed
off quietly.

The next day the _Porpoise_ was taken below the surface, in order to
allow of better speed being made. She was running along, submerged to a
depth of two hundred feet, when there came a sudden jar, and the ship
stopped.

"More trouble!" exclaimed the professor.

He opened the slide covering the bull's-eye windows and looked out. All
about was swirling muddy water.

"Can you see anything?" the inventor called to Jack, who was in the
conning tower.

"We've run into a mud-bank, and are stuck fast," called back the boy.

CHAPTER XIV

DIGGING OUT THE SHIP

"Reverse the engine!" called the professor. "Maybe we can back the ship
out."

Washington set the big screw to revolving in the opposite direction. The
_Porpoise_ shook and shivered but the mud held her fast.

"We must have gone in pretty deep," commented Amos Henderson. "Luckily
it was soft mud instead of a rocky reef or we'd have damaged the ship
beyond repair."

For several minutes the engines were kept on the reverse, but all to no
purpose. The sticky mud was like glue in its holding power and the ship
had buried her prow deep into it.

"I guess we'll have to dig our way out," said the professor, after
taking a careful view of the big mud bank from the conning tower.
"Washington, get out the diving suits and the spades."

"Are we really going out in the water to dig?" asked Tom.

"Of course," said Mr. Henderson. "You'll be as safe as in the ship,
wearing one of my diving suits. We'll all have to help, for it will be
quite a task."

The queer suits were brought out, and the reservoirs in the helmets were
filled with compressed air. It was decided to have Washington remain
within the _Porpoise_, to watch the machinery and start the engine when
the digging was partly done, in order to see if the ship would not pull
herself free when some of the mud had been removed from the prow.

"And we may need Washington for another purpose," said the professor.

"What for?" asked Mark.

"Well, he'll have to stay by the diving tank, to let us in quickly in
case of emergency."

"Do you think there'll be an emergency?" asked Jack.

"You never can tell," was the