stratigraphic intervals
   (System) †Ordovician (485.4 - 443.8 Ma)
     (Series) †Middle (470.0 - 458.4 Ma)
       (Stage) †Caradocian
         1 (Substage) †Actonian + Onnian
         2 (Substage) †Soudleyan-Marshbrookian
         3 (Substage) †Costonian + Harnagian