"That's it," he exclaimed, as he picked it up. "I'd know it in a minute by its shape and weight. Rather light for a cannon ball." But he did not wait to examine it there. There would be time enough for that when he reached the flagship. With a parting look at his unconscious antagonist he started away. "I'm sorry, my dear sir," he exclaimed, sarcastically, as he looked back on reaching the top of the rampart. "You seemed so attached to this shell, I'd like to take you along with it. But as I can only take one at a time, I'll content myself with this." Then he turned his back upon the scene of his contest, and started for his boat as expeditiously as due caution would allow. He met with no obstacle in the way, and found the boat just as he had left it. He threw the shell in the stern, and with a feeling of exultation sprang in after it and seized the oars. A few steady strokes and he was on the way toward the flagship. But there had been a change in those quiet waters while he was on the land. He had not gone many boat lengths from shore before he discovered looming up before him a slowly moving steamer. It was apparently hugging the coast and proceeding with as little noise as possible. "A boat trying to run the blockade!" exclaimed Clif, as he backed water and rested upon his oars. "She'll succeed, too, unless one of our ships should happen to discover her with its searchlight." And then his responsibility, in view of the discovery he had made, flashed upon him. "I must warn the flagship at once," he exclaimed, seizing the oars and sending the boat forward with a spurt. But after a couple of strokes he suddenly stopped again. "What a fool I am!" he exclaimed. "By the time I can row out to the flagship, it will be too late. They must be warned instantly, and there is only one way of doing it." He reached for the signal rockets he had brought at the rear admiral's order. Should he fire them? Those on board the strange boat that was nearly abreast of him did not know that he was there. If he gave the signal it would betray his presence, and no doubt lead to an attack upon himself in his open boat. Clif looked far out to sea for a moment, half hoping to see the flash of the searchlight play upon the water, and lead to the detection of the strange craft. But the delay was only momentary. "It is my duty to warn the ships," he exclaimed, as he set a rocket up in the stern, and drawing a match from his pocket, struck it upon the seat of the boat. "Here goes!" A moment later, with a sharp whirr and a flash of light, the rocket shot up into the air. A second and third followed; then Clif sprang back upon his seat and seized the oars. The signal had been given. He had done his duty at whatever risk there might be to his own safety. CHAPTER XXXI. CAPTURED.