The Coral Island By R M Ballantyne

Fifteen-year-old Ralph, mischievous young Peterkin and clever, brave Jack are shipwrecked on a coral reef with only a telescope and a broken pocketknife between them. At first the island seems a paradise, with its plentiful foods and wealth of natural wonders. But then a party of cannibals arrives, and after that a pirate ship...what is to become of them?