answer. "We are in deep water, and I don't
want any accidents to happen."

In a few minutes all save Washington were in their diving suits and
ready to go out and walk on the bottom of the sea. They entered the
tank, the door was closed, and then water was slowly admitted from the
ocean. When the tank was full, led by the professor, they stepped out on
the muddy floor of the ocean.

At first the pressure of the water at so great a depth bothered them.
But, as we know, the diving suits were reinforced with plates of steel,
and so strong that little more than an extra weight of water was
noticed. They soon became used to it. Each one carried a spade, while
the professor, Andy and the boys each had, slung about their necks by
straps, one of the electric guns.

Cautiously they walked toward the big mud bank. They had to go slowly
because of the weight of the water above them, and because they might at
any minute step into some muck hole and sink down. Fortunately, however,
they found there was a firm bottom right up to where the bank of mud
reared upward.

Turning on the electric lights in their helmets, the voyagers were able
to see quite distinctly. The _Porpoise_ had rammed her nose into the
under-water hill for a distance of about ten feet. It was going to be no
easy matter to get her free, but the divers lost no time.

Vigorously they attacked the big hill of mud. They dug their spades in
and tossed the earth to one side. It was a strange place to work. At
first the weight of water hampered every one, but they soon became used
to it and were able to proceed more rapidly.

From the conning tower Washington kept watch of their progress. When
they had gone in about five feet he started the engines, hoping the
_Porpoise_ might now pull herself free. But the mud still held.

By signs, for it was of course impossible for any one to hear or speak,
attired as they were in helmets and suits, the professor motioned that
they must dig deeper.

Once more they attacked the big mud bank with their shovels. Farther and
farther they went into the muck until it seemed that the nose of the
submarine must be free. But when Washington started the engines it was
obvious that the ship was still held.

Again the digging was resumed. All at once, while every one was wielding
his spade to best advantage, a shadow seemed to cover the water. It
loomed up large and black, and the professor stopped and gazed upward.
What he saw made him