2.2.2 Construction of formal names
Names of formal geological units are compound terms, usually made up of two or three parts. In the case of geological units that are looked upon as single, physical entities the first component of the name is the proper name. For geological units of a collective nature (see Section 1.3), such as a period of time, this is a distinguishing collective name. It may be a geographical term or some other sort of name (see Sections 2.2.3 and 2.2.4) representing the type section, type locality or type area/area of distribution (Section 2.4.5). The second component of two-part names may denote (a) the rank of the unit in the classification system (e.g. group, formation, lithodeme, biozone, etc.), (b) the principle lithology of the unit (e.g. sandstone, basalt, conglomerate, etc.), or (c) the rank and/or distinguishing character of the unit (e.g. nappe, fault, basin, plug, syncline, etc.). In three-part names, the middle part can be a descriptive name placed between the proper or characterizing name and the part signifying rank or lithology. Such three-part names should be used as little as possible.
As a guiding principle, the same proper or characterizing name should not be given to more than one geological unit. Exception may be made for units derived directly from other geological units that have been established. This applies to rootless palaeobasins (Sections 3.7 and 3.7.14.7), escarpments (Section 3.7.12.6), thrusts (Sections 3.9 and 3.9.9.6), geochronological units (Section 4.3), geochronometrical units (Section 4.4), polarity-chronological units (Section 4.6), chronozones (Section 4.2.7) and, in part, diachronous units (Section 4.7).