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