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 Gods!” 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 gods 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 ashore.

Once ashore 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.