Stratum

n. horizontal layer of material; bed of sedimentary rock (Geology); level of society

This article is about the geologic use of the term, for other uses see Stratum (disambiguation) For other uses, see strata (novel) and strata title.In geology and related fields, a stratum (plural: strata) is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural forces. They may extend over hundreds of thousands of square kilometers of the Earth's surface. 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 a kilometer or more. Each band represents a specific mode of deposition -- river silt, beach sand, coal swamp, sand dune, lava bed, etc.
See more at Wikipedia.org...

n. (Geology) stratum, layer of material, bed of sedimentary rock (such as rock, earth, etc.)

n. stratum, horizontal layer of material; bed of sedimentary rock (Geology); level of society

(n.)
A bed or layer artificially made; a course.
  

(n.)
A bed of earth or rock of one kind, formed by natural causes, and consisting usually of a series of layers, which form a rock as it lies between beds of other kinds. Also used figuratively.