has done more to advance and apply sedimentology than any other branch of industrial geology. Critical readers will notice that metres, feet, kilometres, and miles are used indiscriminately throughout the book. Since the oil industry refuses to go metric, the student must quickly learn to correlate the two systems. A conversion scale is included in the first figure. January, 1970 RICHARD C. SELLEY Tripoli, Libya Preface to the second edition I began to write the first edition of this book after spending nearly ten years at university studying and teaching how to diagnose the depositional environments of sedimentary rocks where they crop out at the earth's surface. The first edition was written during the first three months of my five-year sabbatical in the oil industry. From then on a very large part of my time has been spent learning how to diagnose the environments of sediments from bore holes in the sub-surface. This is a far more challenging occupation for there are fewer data, the techniques are quite different, and the economic implications may be immense. The new edition reflects this experience. The introductory chapter includes a -discussion of the techniques of sub-surface facies analysis, and subsequent chapters discuss the criteria by which each environment may be recognized in the sub-surface. Most of the chapters have been modified in one way or another; sections on modern environments have been expanded and some of the case histories have been extensively modified and, for the Captain 'reef', completely rewritten.