Sedimentary rocks are deposited in layers as strata, forming a structure called bedding.
Bedding planes are surfaces that separate one layer from another. Bedding planes can also form when the upper part of a sediment layer is eroded away before the next episode of deposition. Strata separated by a bedding plane may have different grain sizes, grain compositions, or colors. Sometimes these other traits are better indicators of stratification as bedding planes may be very subtle.