strata

Characteristics

Typically, a stratum is generally one of a number of parallel layers that lie one upon another to form enormous thicknesses of strata. The bedding surfaces (bedding planes) that separate strata represent episodic breaks in deposition associated either with periodic erosion, cessation of deposition, or some combination of the two. Stacked together with other strata, individual stratum can form composite stratigraphic units that can extend over hundreds of thousands of square kilometers of the Earth's surface. Individual strata can cover similarly large areas. Strata are typically seen as bands of different colored or differently structured material exposed in cliffs, road cuts, quarries, and river banks. Individual bands may vary in thickness from a few millimeters to several meters or more. A band may represent a specific mode of deposition: river silt, beach sand, coal swamp, sand dune, lava bed, and others.