shallow processes and for the pursuit of more Sediments are now known to undergo deforma­ tion in a wide variety of geological circumstances. quantitative relationships. With these goals in The deforming processes can happen on a vast mind, workers are increasingly drawing on the scale and at all stages before the material be­ principles and methods of the well-established comes fully lithified. In fact, as exploration of the engineering discipline of soil mechanics. earth continues, the widespread extent and im­ All this is beginning to attract wider geological portance of sediment deformation is still being interest. Yet to the newcomer, because progress revealed, for example, below the oceans and has been rapid in recent years, the literature is beneath ice sheets. At the same time, it is still already formidable. The information is scattered, being realized just how varied are the resulting so even an expert on sediment deformation in a structures, and how strikingly similar they can be certain setting may be unaware of analogous to those produced by the deformation of deeply problems and successes in other environments. buried rocks. At the same time, although the same basic prin­ However, there are few precedents to guide the ciples apply in the various geological regimes, a geologist in interpreting structures that formed in subtly different terminology is evolving, which unlithified sediments, or in understanding the can make the subject boundaries hard to cross.