This popularized account of the forthcoming attempt to drill down below the ocean and bring up cores of the earth's mantic is probably the first of its kind. It is written by an expert, a scientist-engineer who is directing the project. He describes the history of the scheme, the purpose (to provide for the first time evidence of what the earth is like inside), and the methods which will be used. Known as the Mohole Operation, it may be as important in its introspective way as any rocket experimentation of today. The book however, which is semi-technical throughout, suffers from a certain dullness which will inspire fewer readers over the possibilities of Mohole drilling than might otherwise have been achieved.