stra·tum /ˈstretəm, ˈstræ-/
  地層,階層
  stra·tum /ˈstretəm, ˈstræt-/ 名詞
  (複strata)層,層聚(生態)
  stratum
  層
  stratum
  層
  Stra·tum n.; pl. E. Stratums L. Strata The latter is more common.
  1. Geol. 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.
  2. A bed or layer artificially made; a course.
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  stratum
       n 1: one of several parallel layers of material arranged one on
            top of another (such as a layer of tissue or cells in an
            organism)
       2: an abstract place usually conceived as having depth; "a good
          actor communicates on several levels"; "a simile has at
          least two layers of meaning"; "the mind functions on many
          strata simultaneously" [syn: level, layer]
       [also: strata (pl)]