This time the blow was heavier. It sent them against the side of the compartment.

"Ice beneath the ocean? Impossible!" exclaimed the Doctor. "Must be rocks!"

Another blow hurled them in the opposite direction. Both realized the gravity of this new peril. If one of these blows caught the craft squarely it would crush the sub like an egg-sh.e.l.l.

But the boat was slowing up. There was hope in that. Dave, attempting to look out of one of the portholes, was thrown to the floor by another shock. And this time the craft seemed to have stuck, for she did not move.

"Where can we be?" asked Dave, rubbing a bruised head.

It was a strange sight which met their eyes as they looked from the conning tower. On every side appeared to be giant pillars of ice.

Between these were narrow water pa.s.sages, while above they could make out a ma.s.s of ice far more opaque than any they had yet pa.s.sed beneath.

"One of two things," said the Doctor. "We are beneath an iceberg or the end of a glacier. Probably a glacier, and the pillars which support it reach to the bottom, which must not be far below us."

"We have driven between two pillars and stuck there like a mouse in a trap," said Dave, "and if we cannot set ourselves free, we are--"

"It must be done!" exclaimed the Doctor. "Start the power slowly and see what the propeller will do."

Dave gave the signal. There followed a harsh, grating sound, but the boat did not move.

"Stuck!" muttered Dave.

"Not so fast." said the Doctor. "There's hope yet. Shut off the power and order all hands aft."

"Now," said the Doctor, when they were a.s.sembled. "We will go to the starboard side, then all together dash to port, and throw our weight against the side. Then turn and rush back--we want to make her roll. Are you ready? Go!"

The craft stirred a trifle at the shock. The second attempt seemed to promise still better. After they had repeated the operation half a dozen times, they were getting considerable side-wise movement out of the trapped submarine.

"Now," said the Doctor, "start the power slowly, engine reversed. The instant she is free, shut off the power. On the precision of this operation depends all our lives, for should the propeller strike one of those pillars it will be torn away and our hope of escape gone."

Dave's hand trembled as he moved the lever. For one second the propeller spun around. Then, with a shudder, the craft started backward. That instant Dave shut off the power. The submarine drifted free. So far, they were safe.

The Doctor consulted his watch.

"Time of low tide," he observed "Guess we should be able to rise and get some air. Try it."

Slowly they rose to the surface, and there the craft rested.

It was an eager throng that rushed from the conning-tower and it was a wonderful and awe-inspiring sight which met their gaze.

"Cathedral of the Polar G.o.ds!" exclaimed the Doctor. And, indeed, so the great cavern seemed to be. Great pillars of ice, not yet worn away by the wash of water, supported giant arches of ice, blue as a mid-June night.

The least echo was echoed and reechoed through the vast corridors. The murmur of distant waves seemed to come from everywhere.

"What I want to know," said Dave, "is, which way is out. The careless G.o.ds seemed to have neglected to mark the exits."

"We'll find an exit," said the Doctor, "and we'd better be about it, for it'll be much easier at low-tide than at high."

The engine was started, and slowly they steered their way through countless aisles and broad halls, but the finding of the way out did not seem so easy after all. They had penetrated far enough into the cavern to hide them from the pale outer moonlight, and they were not certain that their course was not taking them farther from it.

Dave was thinking of turning about when the sub came to a stop with a suddenness which threatened to pitch the party into the sea.

"What now?" demanded the Doctor.

Ordering the power shut off, then flashing a light before them, Dave exclaimed: "A beach, a sandy beach!" Then, with the enthusiasm of a boy, he sprang forward, leaping into shallow water and wading ash.o.r.e.

Once ash.o.r.e he flashed his light about in the icy caverns which left but a narrow sandy beach. Then, with a cry of horror, he sprang backward.

Before him towered an immense hairy monster, with tusks three times the length of a man's arm.

The instant the cry had left his lips, he knew the laugh was on him. But the cry had gone forth, echoing through the corridors. It brought the jackies and the Doctor splashing through the water to his rescue.

"Only a frozen mastodon," he grinned sheepishly, as they came to his side. "Guess he's been dead ten thousand years, to say the least. But honest, doesn't he look natural standing there in the ice?"

He flashed the light suddenly upon the ice-encased monster, and the jackies jumped, as if they, too, expected to be attacked.

"A beautiful corpse, I'd say," exclaimed one of them.

"A most remarkable specimen," commented the Doctor. "I've heard of cases like this, but never saw one before."

"Say!" exclaimed Jones. "If we could only get him out of here like that and put him down in alcohol, we'd have a side-show that would make Barnum jump out of his grave!"

"Not a bad idea," said the Doctor. "The only hitch would be getting him out of here."

As Dave backed away for a better view, his foot struck something hard.

Flashing his light upon it, he found it to be the skull and tusks of a walrus. They were as black as coal.

"I've made a find!" he exclaimed. "These tusks we may take with us, and old ivory is about as valuable as precious stones."

The discovery seemed to waken the Doctor to their peril.

"That walrus," he said, "wandered in here and was drowned by the rising tide. He can breathe under water, but cannot stay down over ten minutes.

We can't breathe at all under water. The tide is setting in."

These words sent the crew scurrying back to the submarine. Already the tide had risen sufficiently to float the craft. All hands hastened to re-embark.

"If we set our course directly at right-angles to this beach and keep it there," said Dave, "it should bring us to safety."

This was done, and, after many a turn and twist, they caught a gleam of light. Submerging, they were soon beneath the ice-floe once more. With a sigh of relief, Dave gave the order to rise at the first water-hole.

There they might take their bearings.

A half-hour later the party was gathered on the deck gazing away at an island above which there towered a snow-capped mountain. Down the side of the mountain might be distinguished the winding, blue course of a great glacier.

"Our glacier!" said Dave. "Some glacier, I'll say!"

"Our glacier!" repeated a jackie. "Long may she glide!"

The course was set at an angle to the island. This would carry them past any treacherous sand-bars. They would then take another tack and resume their former course.

At a few minutes before noon that day they rose far from the island. The sun, a pale yellow disk, shone through a thin haze close to the surface of the pack. And yet it was high noon. This was, perhaps, to be their last bearing taken by the light of the sun. Henceforth, the moon and the stars must guide them. Whereas all former polar expeditions were carried forward only during the summer months, when the sun shone night and day, they, as well as their rivals, must drive on straight into the deep mysteries of the dreaded Arctic night.