But the Frenchman did not reply. He looked round the horizon with a puzzled expression, and, putting his hand to his ear, appeared to be listening intently. "Hark, captain! What is that?" he cried. CHAPTER VIII Carew listened, and heard a low, rumbling sound like distant thunder. "Thunder out of a cloudless sky! That is strange." "That is no thunder, captain," said Baptiste, with a scared look, "but what it is I know not." The sound became louder. It did not seem to be approaching from any direction, but to be everywhere--around, below, above--filling all space. Then it swelled to a great roar, as of the rolling of thousands of drums. The air trembled at the sound, and the surface of the sea no longer reflected the blue sky above, but, appearing like a mirror over which one has breathed, vibrated into myriads of wrinkles and gyrating rings. Soon the water began to be greatly disturbed, and raved and foamed about the vessel as if she were floating in a boiling caldron. Then occurred an appalling prodigy. First, louder than loudest thunder, was heard a deafening explosion, and immediately the sea leapt up, not in waves, but in steep pyramids of water, piling itself up in domes, as if some mighty force were thrusting it up from below. The yacht pitched wildly into the confused whirl till she was nigh to break up with the violence of the shocks, and the water poured over her decks in masses, threatening to swamp her. Hollow whirlpools opened out suddenly in front of her, seeking to engulf her: a fearful spectacle to behold, which might make even the bravest men go mad with fright. Then came another explosion, and the superstitious Spaniards, holding on to the rigging for dear life, shrieked with abject terror as they saw the limpid sea suddenly thicken and change its colour to a dark, sulphurous yellow. There was an odour of sulphur in the air, and the sun was shining through a sickly yellow haze. The crew, who would have done their duty with cool courage in a hurricane, were completely unnerved by this alarming portent. The two men forward thought that the fiend himself had opened hell under them to swallow up their sinful souls; they prayed and blasphemed in turns. The French mate, white to his lips and trembling, clutched the rigging, with his eyes closed. Carew alone, though his cheeks were pale, was calm. Holding on to the bulwark to prevent himself from being thrown overboard by the violent leaping of the yacht, he looked around him with a resolute expression. He would fight bravely for his life, but he had no fear of death. In the midst of this turmoil a strong wind suddenly arose.