[WARN-A001] - No package description in UML model The classic "Geologic Timescale" comprising an ordered, hierarchical set of named "eras" is an example of an Ordinal Temporal Reference System. It may be calibrated with reference to a numeric Temporal Coordinate System, but is in principle defined independently. Used for pre-Ediacaran and Pleistocene / Holocene boundaries in the standard timescale The association of an era with a stratotype is optional. In the GSSP approach recommended by ICS for the Global Geologic Timescale, Unit Stratotypes are not used. Rather, the association of an Era with geologic units and sections is indirect, via the association of an era with Boundaries, which are in turn tied to Stratotype Points, which occur within host Stratotype Sections. Note that the "German School" defines stratigraphic eras conceptually, without reference to stratotypes.