Within half an hour the gig had reached the mouth of the cave. As the coxswain had predicted, the seas ran into the lofty entrance. Elsewhere the surf fell whitely, but through the arch the waves rolled unbroken into a heavy stillness. Only as the boat hovered for a moment at the face of the cliff could the exploring party hear, far within, the hollow boom that told of breakers on a distant, subterranean beach.

"Run her in easy," came the captain's order. "Keep a sharp lookout for hidden rocks."

To the whispering plash of the oars they moved from sunlight into twilight, from twilight into darkness. Of a sudden the oars jerked convulsively. A great roar had broken upon the ears of the sailors; the invisible roof above them, the water heaving beneath them, the walls that hemmed them in, called, with a multiplication of resonance, upon the name of Darrow. The boat quivered with the start of its occupants. Then one or two laughed weakly as they realised that what they had heard was no supernatural voice. It was the captain hailing for the marooned man.

No vocal answer came. But an indeterminable space away they could hear a low splash followed by a second and a third. Something coughed weakly in front and to the right. Trendon's hand went to his revolver. The men sat, stiffened. One of them swore, in a whisper, and the oath came back upon them, echoing the name of the Saviour in hideous sibilance.

"Silence in the boat," said the captain, in such buoyant tones that the men braced themselves against the expected peril.

"Light the lantern and pass it to me," came the order. "Keep below the gunwale, men."

As the match spluttered: "Do you see something, a few rods to port?" asked the captain in Trendon's ear.

"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.

"Dr. Trendon, are you all right?" he shouted.

"Yup," answered a choked voice. "Cubbing oud dow."

Again the funnel was darkened. A pair of feet appeared; then the surgeon's chunky trunk, his head, and the lantern. Once, twice, and thrice he inhaled deeply.

"Phew!" he gasped. "Thought I was tough, but--Phee-ee-ee-ew!"

"Did you find--"

"No, sir. Not Darrow. Only a poor devil of a seal that crawled in there to die."

The exploration continued. Half a mile, as they estimated, from the open, they rea............