Stratum

strā′tum, n. a bed of earth or rock formed by natural causes, and consisting usually of a series of layers: any bed or layer:— pl. Strā′ta .— adj. Strat′iform , formed like strata.— ns. Stratig′rapher , Stratig′raphist , a student of stratigraphical geology.— adjs. Strati graph′ic , -al , concerned with the relative position of the strata forming the earth's crust.— adv. Strati graph′ically .— n. Stratig′raphy , the order and position of the stratified groups: the study or description of these, descriptive geology.— adj. Strā′tose , arranged in layers, stratified.— n.pl. Strat′ūla . thin layers in rock-strata. [L. stratum — sternĕre , stratum , to spread out.]