An actual rock succession, chosen at a particular locality (the type locality) to act as the standard comparison for all other chronostratigraphic or lithostratigraphic units of its ilk. Generally, the type section of a stratigraphic unit should be the rock succession originally so designated and described (the holostratotype), but circumstances may require amendment (see lectostratotype; neostratotype), or amplification (see parastratotype; hypostratotype). However, although many similar sequences may exist, only a single stratotype at any one time can act as the standard. See also boundary-stratotype; composite-stratotype; component-stratotype; type area.