2.3 Names of informal units
2.3.1 The reason for having informal units, their use and status
Informal units can be introduced for temporary use (a) when carrying out geological mapping, (b) during ongoing scientific, engineering or economic investigations, (c) when preliminary research results are being published, (d) when writing internal reports, theses, etc., that are not going to be published, and (e) for more lasting use when for various reasons it is not practical to erect formal units.
Informal units need not be erected in the manner required for formal units in this Code (Section 2.4) or in ISSC (1976).
Irrespective of how they are defined or documented, all names given to geological units that are described and named in internal reports, unpublished undergraduate or doctorate theses, compendiums, textbooks, circulars, guide books (except those published in large editions), etc., are to be looked upon as being informal (see Section 2.4.14).