Dryas

Part of the characteristic threefold late-glacial sequence of climatic change and associated deposits following the last, Devensian, ice advance and prior to the current, Flandrian, interglacial. The colder Dryas phases mark times of cold, tundra conditions throughout what is now temperate Europe (Britain did not experience the Older Dryas). The Oldest Dryas (Dryas I/Pollen Zone Ia) lasted from about 16 000 to 15 000 years bp, with tundra-grassland characterized by Dryas octopetala (mountain avens); the Older Dryas (Dryas II/Pollen Zone Ic) from 12 300 to 11 800 years bp; and the Younger Dryas (Dryas III/Pollen Zone III) from about 11 000 to 10 000 years bp. The series shows upper- and lower-clay deposits rich in remains of Dryas octopetala, interspersed with deposits of lake mud, evidence of cool temperate flora, such as birches. See Pleistocene chronology.