<P> Sedimentary environments usually exist alongside each other in certain natural successions . A beach, where sand and gravel is deposited, is usually bounded by a deeper marine environment a little offshore, where finer sediments are deposited at the same time . Behind the beach, there can be dunes (where the dominant deposition is well sorted sand) or a lagoon (where fine clay and organic material is deposited). Every sedimentary environment has its own characteristic deposits . The typical rock formed in a certain environment is called its sedimentary facies . When sedimentary strata accumulate through time, the environment can shift, forming a change in facies in the subsurface at one location . On the other hand, when a rock layer with a certain age is followed laterally, the lithology (the type of rock) and facies eventually change . </P> <P> Facies can be distinguished in a number of ways: the most common are by the lithology (for example: limestone, siltstone or sandstone) or by fossil content . Coral for example only lives in warm and shallow marine environments and fossils of coral are thus typical for shallow marine facies . Facies determined by lithology are called lithofacies; facies determined by fossils are biofacies . </P> <P> Sedimentary environments can shift their geographical positions through time . Coastlines can shift in the direction of the sea when the sea level drops, when the surface rises due to tectonic forces in the Earth's crust or when a river forms a large delta . In the subsurface, such geographic shifts of sedimentary environments of the past are recorded in shifts in sedimentary facies . This means that sedimentary facies can change either parallel or perpendicular to an imaginary layer of rock with a fixed age, a phenomenon described by Walther's Law . </P> <P> The situation in which coastlines move in the direction of the continent is called transgression . In the case of transgression, deeper marine facies are deposited over shallower facies, a succession called onlap . Regression is the situation in which a coastline moves in the direction of the sea . With regression, shallower facies are deposited on top of deeper facies, a situation called offlap . </P>

Who formulated the principles describing the layers of sedimentary rocks