Sedimentary facies are the characteristics of a given layer of sedimentary rock, including organic and inorganic deposits. The facies of sedimentary rocks help date layers, and they are also important in describing the environment in which those rocks were formed.
When exposed in a weathering mountainside, a stream or a quarry, sedimentary strata, or layers, can be seen easily. Each stratum's facies can be compared to the geological record to determine its probable age, its point of origin and the likelihood of finding certain types of artifacts or fossils within the layer. Facies are also useful for determining parts of Earth's history, such as the details of continental drift.