It was about four o'clock one morning that Washington felt a slight jar
to the submarine.

"Hope we ain't goin' to hit no more battleships," he said.

He glanced at the speed-indicating gage. To his surprise it stood at
zero. The craft was not moving forward a foot! Yet the engines were
going at half speed!

In great alarm Washington shut off the power and ran to acquaint
Professor Henderson with the news.

"Suffin's ketched us!" cried the colored man.

"Nonsense!" said the inventor, yet he seemed alarmed as he slipped on
his clothes and hastened to the conning tower.

He peered ahead along the path of water illuminated by the glare of the
searchlight, but nothing was to be seen. Then he started the engine,
increasing the speed gradually until the big screw in the shaft revolved
more than one thousand times a minute. Still the _Porpoise_ never
stirred. She remained in the same position, as if some giant hand
grasped her.

"Reverse the engine," said the professor.

Washington did so. To the surprise of both of them the ship shot
backward like a frightened crab.

"Now forward!" exclaimed the old inventor.

But this time the _Porpoise_ did not move. It was as if she was up
against a stone wall.

"What's the matter?" asked Mark, who had been awakened by the excitement
on board.

"I do not know," replied Mr. Henderson gravely. "Something mysterious
has occurred. We can go no further!"

CHAPTER VIII

ASHORE IN THE DARK

"Stop the engine," the captain commanded after he had peered through the
lens in the conning tower for some time. "We must see what is the
matter."

He glanced at the depth gage and noted that they were now four hundred
feet below the surface. Then he consulted some charts.

"There is a depth of one thousand feet about here," he remarked. "Lower
the ship, Washington. Let us see if by getting on the ocean bed we can
get away from this obstruction."

The colored man opened wider the sea cocks by which the tanks were
filled. The increased ballast sunk the _Porpoise_ still lower, and, in a
few minutes a slight jar told the navigators that they were on the
bottom of the ocean.

"Now we will see if we have cleared the obstruction," said the
professor.

He started the big screw to revolving, but the ship did not move. It
shivered and trembled throughout its length but remained stationary.

"Maybe dar's a debil fish what hab circumulated dis ship in de exteror
portion ob his anato