#geological_period__period  a unit of geological time during which a system of rocks formed; "ganoid fishes swarmed during the earlier geological periods"
  supertype:  geological_time__geologic_time__geologictime  the time of the physical formation and development of the earth (especially prior to human history)
  instance:  Quaternary_period  Tertiary_period  Cretaceous_period  Jurassic_period  Triassic_period  Permian_period  Carboniferous_period  Pennsylvanian_period  Missippian_period  Devonian_period  Silurian_period  Ordovician_period  Cambrian_period
  part:  epoch
  part of:  geological_era
  subtype:  ice_age__iceage__glacial_period__glacialperiod__glacial_epoch  any period of time during which glaciers covered a large part of the earth's surface

No statement uses or specializes geological_period; click here to add one.