Simulation. "why simulate?" we might ask. dan tetzlaff and john harbaugh answer that question in simulating clastic sedimentation, and answer it effec tively. readers will have no trouble following this well-documented, clear ex pose on clastic-sedimentation simulation. the sophistication in simulation since 1970, compared to the early work, is enormous. the development and availability of hardware, especially graphics, has made such advancement pos sible. the authors' presentation allows us to share in this exciting new approach to geological problem solving. the book contains a glossary, notation conven tion, program listings, plenty of illustrations, and chapter summaries to en lighten the users. everything is readily available to make this a self-contained, how-to and how-to-interpret book. after introducing the subject of simulation, the authors take the reader step-by-step through the computation and reasoning of the erosion, transporta tion, and deposition of clastic sediments. fluid flow, transport, boundary con ditions, and space and time are all explained, and details are given as to how each of these factors were accounted for in the simulation. the simulation is compared to different known situations, such as braided streams and deltas, for assessment as to realism. the final chapter gives two real-world applications where a simulated model is compared to the simpson canyon field in north ern alaska and the golden meadow field in southern louisiana. from these simulations was gained some understanding of the conditions under which c- ix series editor's foreword tain sedimentary units were formed.