"You say the last entry is June 7th?" asked Barnett, as the boat entered the light surf.

Trendon nodded.

"That was the night we saw the last glow, and the big burst from the volcano, wasn't it?"

"Right."

"The island would have been badly shaken up."

"Not so violently but that the flag-pole stood," said the captain.

"That's true, sir. But there's been a good deal of volcanic gas going. The man's been penned up for four days."

"Give the fellow a chance," growled Trendon. "Air may be all right in the cave. Good water there, too. Says so himself. By Slade's account he's a pretty capable citizen when it comes to looking after himself. Wouldn't wonder if we'd find him fit as a fiddle."

"There was no clue to Ives and McGuire?" asked Barnett presently.

"None." It was the captain who answered.

The gig grated, and the tide being high, they waded to the base of the cliff, Barnett carrying his precious explosives aloft in his arms.

"Here's the spot," said the captain. "See where the water goes in through those crevices."

"Opening at the top, too," said Trendon.

He let out his bellow, roaring Darrow's name.

"I doubt if you could project your voice far into a cave thus blocked," said Captain Parkinson. "We'll try this."

He drew his revolver and fired. The men listened at the crevices of the rock. No sound came from within.

"Your enterprise, Mr. Barnett," said the commander, with a gesture which turned over the conduct of the affair to the torpedo expert.

Barnett examined the rocks with enthusiasm.

"Looks like moderately easy stuff," he observed. "See how the veins run. You could almost blow a design to order in that."

"Yes; but how about bringing down the whole cave?"

"Oh, of course there's always an element of uncertainty when you're dealing with high explosives," admitted the expert. "But unless I'm mistaken, we can chop this out as neat as with an axe."

Dropping his load of cartridges carelessly upon a flat rock which projected from the water, he busied himself in a search along the face of the cliff. Presently, with an "Ah," of satisfaction, he climbed toward a hand's breadth of platform where grew a patch of purple flowers.

"Throw me up a knife, somebody," he called.

"Take notice," said Trendon, good-naturedly, "that I'm the botanist of this expedition."

"Oh, you can have the flowers. All I want is what they grow in."

Loosening a handful of the dry soil, he brought it down and laid it with the explosives. Next he called one of the sailors to "boost" him, and was soon perched on the flat slant of a huge rock which formed, as it were, the keystone to the blockade.

"Let's see," he ruminated. "We want a slow charge for this. One that will exert a widespread pressure without much shattering force. The No. 3, I think."

"How is that, Mr. Barnett?" asked the captain, with lively interest.

"You see, sir," returned the demonstrator, perched high, like a sculptor at work on some heroic masterpiece, "what we want is to split off this rock." He patted the flank of the huge slab. "There's a lovely vein running at an angle inward from where I sit. Split that through, and the rock should roll, of its own weight, away from the entrance. It's held only by the upper projection that runs under the arch here."

"Neat programme," commented Trendon, with a tinge of sardonic scepticism.

"Wait and see," retorted Barnett blithely, for he was in his element now. "I'll appoint you my assistant. Just toss me up that cartridge: the third one on the left."

The surgeon recoiled.

"Supposing you don't catch it?"

"Well, supposing I don't."

"It's dynamite, isn't it?"

"Something of the same nature. Joveite, it's called."

Still the surgeon stared at him. Barnett laughed.

"Oh, you've got the high explosives superstition," he said lightly. "Dynamite don't go off as easy as people think. You could drop that stuff from the cliffhead without danger. Have I got to come down for it?"

With a wry face Trendon tossed up the package. It was deftly caught.

"Now wet that dirt well. Put it in the canvas bag yonder, and send one of the men up with it. I'm going to make a mud pie."

Breaking the package open, he spread the yellow powder in a slightly curving line along the rock. With the mud he capped this over, forming a little arched roof.

"To keep it from blowing away," surmised Trendon.

"No; to make it blow down instead of blowing up."

"Oh, rot!" returned the downright surgeon. "That pound of dirt won't make the shadow of a feather's difference."

"Won't it!" retorted the other. "Curious thing about high explosives. A mud-cap will hold down the force as well as a ton of rock. Wait and see what happens to the rock beneath."

He slid off his perch into the ankle-deep water and waded out to the boat. Here he burrowed for a moment, presently emerging with a box. This he carried gingerly to a convenient rock and opened. First he lifted out some soft padding. A small tin box honey-combed inside came to light. With infinite precaution Barnett picked out an object that looked like a 22- calibre short cartridge, wadded some cotton batten in his hand, set the thing in the wadding, laid it on the rock, carefully returned the small box to the large box and the large box to the boat, took up the cartridge again and waded back to the cliff. They watched him in silence.

"This is the little devil," he said, indicating his delicate burden. "Fulminate of mercury. This is the stuff that'll remove your hand with neatness and despatch. It's the quickest tempered little article in the business. Just give it one hard look and it's off."

"Here," said Tren............