Gradual lateral changes in the type of sedimentary rock can occur within a single layer. Each facies grades laterally into another that formed at the same time but in a different environment. Bedding planes - interfaces between the strata. Generally form in a horizontal configuration, but there are exceptions. Termination of a set of strata by another set of inclined layers.
Ridges form at right angles to the current direction.
The remains of prehistoric life. Rapid burial a condition of preservation. Hard parts not eaten by scavengers are preserved.