Designating a stratigraphic stage or series of rocks corresponding to the lowermost Devonian and (originally) the uppermost Silurian; of or relating this stage or series.
Chiefly with the. The Downtonian stage; the series of rocks dating from this time.
Late 19th century. From Downton, the name of a civil parish in the extreme north of Herefordshire, where this stratigraphic stage is found + -ian.