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."