Writers whose subject is the sea must suffer from comparison with Rachel Carson's two contemporary science classics. Mr. Cromie, a sailor/author, writes well enough to satisfy the general reader and what he lacks in style he makes up for in thoroughness. This book expands his well received Exploring the Secrets of the Sea (1962) and he goes into more details of the sea's origin and that of its animal and plant life. Much of the recent theorizing and experimentation by marine biologists and oceanographers is summarized here and a final chapter includes comment on conservation of this resource. The bibliography is selective, made up for the most part of widely recommended popular books.