While we were all looking over the side, what had hitherto appeared to be a huge piece of rock began to move, and the piercing, savage eyes, and cruel jaws of a vast shark approached the canoe.  I felt a shudder run through my frame as I saw the monster darting out of his ambush. "Give way!" cried Cousin Silas; "he means mischief."  The doctor and I plied our paddles.  The brute made a dash at mine, and almost bit it in two.  Away we went as fast as we could towards the shore, pursued by him.  We shouted as loud as we could and splashed our oars about, to frighten him away; but he seemed in no way disposed to be alarmed. Silva, hearing our shouts, now came paddling toward us.  Jack Shark, however, seemed resolved to play us a trick if he could.  Swimming off to a short distance, he darted back, clearly with the intention of upsetting the canoe.  Cousin Silas turned her away from him just in time, and giving the gentleman a smart blow over the snout, made him think better of his intention.  Silva coming up at the same moment, so distracted his attention that we reached the shore without his succeeding in doing us any material damage.