#soil_horizon  a layer in a soil profile
  supertype:  horizon  a specific layer or stratum of soil or subsoil in a vertical cross section of land
  part of:  profile.cross_section
  subtype:  A-horizon__A_horizon  the top layer of a soil profile; usually contains humus
  subtype:  B-horizon__B_horizon  immediately below the A-horizon; contains deposits of organic matter leached from surface soils
  subtype:  C-horizon__C_horizon  beneath the B-horizon and above the bedrock; consisting of weathered rock

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