“Pair of green lights,” said Trendon.  “Eyes. Seals!”

“Seals!  Seals!  Seals!” shouted the walls, for the surgeon had suddenly released his voice.  And as the mockery boomed, the green lights disappeared and there was more splashing from the distance.  The crew sat up again.

The lantern spread its radiance.  It was reflected from battlements of fairy beauty.  Everywhere the walls were set, as with gems, in broad wales of varied and vivid hues.  Dazzled at first, the explorers soon were able to discern the general nature of the subterranean world which they had entered.  In most places the walls rose sheer and unscaleable from the water.  In others, turretted rocks thrust their gleaming crags upward.  Over to starboard a little beach shone with Quaker greyness in that spectacular display.  The end of the cavern was still beyond the area of light.

“Must have been a swimmer to get in here,” commented Trendon, glancing at the walls.

“Unless he had a boat,” said the captain.  “But why doesn’t he answer?”

“Better try again.  No telling how much more there is of this.”

The surgeon raised his ponderous bellow, and the cave roared again with the summons.  Silence, formidable and unbroken, succeeded.

“House to house search is now in order,” he said.  “Must be in here somewhere—­unless the seals got him.”

Cautiously the boat moved forward.  Once she grazed on a half submerged rock.  Again a tiny islet loomed before her.  Scattered bones glistened on the rocky shore, but they were not human relics.  Occasional beaches tempted a landing, but all of these led back to precipitous cliffs except one, from the side of which opened two small caves.  Into the first the lantern cast its glare, revealing emptiness, for the arch was wide and the cave shallow.  The entrance to the other was so narrow as to send a visitor to his knees.  But inside it seemed to open out.  Moreover, there were fish bones at the entrance.  The captain, the surgeon, and Congdon, the coxswain, landed.  Captain Parkinson reached the spot first.  Stooping, he thrust his head in at the orifice.  A sharp exclamation broke from him.  He rose to his feet, turning a contorted face to the others.

“Poisonous,” he cried.

“More volcano,” said Trendon.  He bent to the black hole and sniffed cautiously.

“I’ll go in, sir,” volunteered Congdon.  “I’ve had fire-practice.”

“My business,” said Trendon, briefly.  “Decomposition; unpleasant, but not dangerous.”

Pushing the lantern before him, he wormed his way until the light was blotted out.  Presently it shone forth from the funnel, showing that the explorer had reached the inner open space.  Captain Parkinson dropped down and peered in, but the evil odour was too much for him.  He retired, gagging and coughing.  Trendon was gone for what seemed an interminable time.  His superior officer fidgeted uneasily.  At last he could stand it no longer.