docs: def _create_skeleton_1(sheets):
      """
      Top level: {"chronData", "paleoData"}
      Fill in paleoData/chronData tables with N number of EMPTY measurement and models.
  
      :return list: Blank list of N indices
      """
      logger_excel.info("enter create_skeleton_main")
  
      # Table template: paleoData
      template_paleo = {"paleoMeasurementTable": [], "paleoModel": []}
      template_chron = {"chronMeasurementTable": [], "chronModel": []}
  
      num_chron = {}
      num_paleo = {}
      paleo = []
      chron = []
  
      # Get table counts for all table types.
      # Table types: paleoData, chronData, model, meas, dist, summary, ensemble
      for sheet in sheets:
          pc = sheet["paleo_chron"]
  
          # Tree for chron types
          if pc == "chron":
              num_chron = _get_table_counts(sheet, num_chron)
          elif pc == "paleo":
              num_paleo = _get_table_counts(sheet, num_paleo)
  
      # Create metadata skeleton for using out table counts.
      paleo = _create_skeleton_2(paleo, "paleo", num_paleo, template_paleo)
      chron = _create_skeleton_2(chron, "chron", num_chron, template_chron)
  
      logger_excel.info("exit create_skeleton_main")
      return paleo, chron