Lionel and Patricia Fanthorpe 
Unsolved Mysteries of the Sea [PDF ebook] 

Seas and oceans cover most of the Earth’s surface, yet we know less about what lies beneath them than we do about stars and planets millions of miles away. The seas are filled with intriguing mysteries: How were they formed? What gave rise to stories of sirens, mermaids, and mermen? Where did the old pirates and buccaneers hide their treasure? The answers to these questions and more can be found in Unsolved Mysteries of the Sea.