"Don't know!"

At that moment a trickling thrill went through the American. A long dark motionless shadow lay in the water straight in front of him. He stopped swimming suddenly.

"Stop, Greer! Straight ahead!" he warned in a low tone, easing himself carefully up on his buoy for a better look.

By this time the swimmers were nearly together and all three stared ahead with painful intentness.

"That dark thing?" inquired Greer in an undertone,

"Yes, we ought to have a knife apiece."

"I never saw a shark lying still," panted Caradoc straining his eyes.

"Say, that's a little streak of seaweed," decided Farnol, beginning to move toward it.

Then all three perceived it was merely seaweed. The shark-like illusion disappeared completely the moment someone doubted it.

"Who cried out sharks anyway?" demanded Smith of Madden.

"Greer there warned me--he yelled 'school of sharks.'"

"Where did you see them?" inquired Caradoc of Farnol.

"You shouted school of sharks to me yourself," defended Greer.

"I! I!" puffed Caradoc, whose spurt had blown him badly. "I said nothing about sharks!"

"Well, what did you say?" demanded Greer.

Caradoc thought back fretfully. "I said we were running into a _cul de sac_."

"A cool de sock!" repeated Greer with irritation. "What did you want to say 'cool de sock' for?"

"I was calling to a gentleman," panted Smith with an edge of temper in his tone, "and here you've swung us clear off our bearings because you didn't know a common French phrase----"

"French! I'm no Frenchman! Why don't you talk English!"

The two tired, worried, overheated men were rapidly brewing a quarrel, when Madden interrupted.

"Look how close we are to that schooner! If somebody would raise another shark alarm, we'd land plump on her decks."

"Yes, but this Zulu here has run us straight into a loop of seaweed it'll take two hours' swimming to get out of--_cul de sac_, school of sharks! Why the two phrases scarcely resemble each other!"

Madden turned longing eyes toward the motionless schooner that was not more than three-quarters of a mile distant. "Say, it's too bad to turn around and swim away from that vessel!" he lamented wearily, "and this sun is fierce!"

"I say let's try going through!" encouraged Greer.

"It'll be--difficult," warned Caradoc.

"Won't swimming clear around the earth be difficult?" demanded Greer hotly.

"Proceed," agreed Caradoc tersely. "It's all one to me."

The boys adjusted their floats and once more began their weary labor, all three disgruntled at the false alarm. As they worked their way forward, clumps of seaweed, similar to the first they had seen, thickened in their path. After a long swim in and out, they reached a point where these floating masses coalesced into an island, or a continent, that swung far back toward the barge in the segment of a great semicircle. Fortunately there were still open channels in this main field, and one of them led toward the schooner. They struck out up this estuary, which presently became so narrow that they were forced to travel single file. Occasionally their kicking feet would strike slimy filaments in the water, but for a while the channel cheered the swimmers, for they could now see they were making progress toward the ship.

Ten minutes later, however, they reached the end, and an inexorable continent of slime lay between them and their goal. Madden paused in the last yard of clear water, hung to his buoy, his big biceps flattened on the canvas cover and slowly blistering in the sun.

"All right, boys, close up," he panted; "let's stay in helping distance of each other."

"Shall we try to take our buoys through, sir?" inquired Greer.

"We'll start with them."

"Don't try to use your legs in the weed," warned Caradoc. "Don't kick; you'll get tangled."

"We'll experiment and work through the best way we can. If it turns out too bad, we can turn back, that's one consolation."

Just then, under Madden's astonished eyes, a queer thing happened. The long open tongue of the sea which they had just entered, silently closed up. It seemed to close very slowly, and yet it was accomplished in an amazingly brief time. Some dull movement in the Sargasso current had blocked the adventurers with sinister precision. Madden felt the hot slimy mass close softly around him.

It was now as easy to go forward as to return.

CHAPTER VII

TRAPPED

There was something so sinister in this silent closing of all avenue of retreat that for a moment Madden was dismayed, then he struck out toward the schooner with a certain bold weariness.

As an experiment he threw his buoy ahead of him by a snap of wrist and forearm, then tried to swim to it. The long yielding growth slid under and around him, but it took all the dash out of his stroke. He pawed his way forward with his arms, legs stretched out idle. A thousand wet sticky fingers dragged their length over his body, retarding, clogging, holding him. It left him stranded like a bug in gelatine. His flesh crawled at this slimy swimming, he shrank from it, and it sapped his heart and strength.

The only stroke possible was the overarm, and his hands fell with a gummy plop instead of the heartsome splash of open water. By the time he reached his buoy and threw it again, he regretted miserably that he had not swum the clean water route if it were five miles farther.

By the time he had thrown his buoy twice, he could hardly advance it a yard beyond his reach; finally it simply slushed along the surface. The sun seemed much hotter in this congestion than in the open sea.

Behind him came his two men in a queer snakelike procession of plopping buoys and wriggling bodies. Ahead of them the seaweed stretched, apparently all the way to the schooner. As they worked their way through the scum of many seas, the noon sun broiled their backs into thin water blisters, and stewed saline odors out of the clammy life about them.

Once Madden's hand struck a yellowish line of algae and a score or two of little jelly-like insects writhed into the grass below. One of these things touched the swimmer's arm and gave the boy a stinging sensation.

He knocked it off desperately and pushed on.

Presently his shoulder muscles ached and burned so keenly, he could no longer continue the overarm. Then he took the buoy in both hands, held it straight out, thrust it edge down into the oozy substance, used it as a kind of anchor and drew it to him. At first this technique seemed to advance him somewhat, but presently he appeared merely to disturb the viscous mass without going forward. He grew acutely discouraged; his back, shoulders, cramped, ached and burned. The brilliantly lighted schooner seemed to regress as he progressed. The sun was like an auger boring into the back of his head. His mind began to wander again, and a sudden fear came on him lest he should go insane out in this horrible slime.

A fiery burning on his right foot jerked him back out of his half delirium, and he knew that an insect of the same kind he had seen a few minutes before had stung him. He kicked it off convulsively, but the thrust of his foot brought a wash of new stings.

All of a sudden, his patience, endurance, pluck seemed to give out. This new torture made him as unreasonably frantic as a baby. He kicked furiously. He scraped the toe nails of one foot against the flesh of the other leg. As he did so the animalculae settled on the abraded skin, like streaks of melted steel. The boy doubled up, like a grub worm covered with ants, fighting, scraping, twisting, squirming. He writhed, beat, scratched, this great hundred and sixty pound animal fighting an enemy that would weigh about twenty to the gram.

He heard a shout from Caradoc, a question from Greer, then his insane struggles carried him under the surface of the clammy seaweed. The seaweed, infested with stinging insects, closed over his form like a wave of fire.