Of, relating to, or designating a stratigraphic stage in western Europe represented by limestone beds in the region of Mons in Belgium, now usually regarded as partly equivalent to the Danian and placed at the bottom of the Tertiary, below the Thanetian or (in Belgium) the Landenian, but sometimes differentiated from and placed above the Danian. Also as noun (usually with the).
The Montian was formerly sometimes regarded as the last stage of the Cretaceous.
Late 19th century; earliest use found in American Naturalist. From French montien from Mont-, Mons, post-classical Latin form corresponding to French Mons, Dutch Bergen, the name of a town in south-west Belgium + -ien.