A warm period that occurred during the final stages of the Devensian glaciation that began abruptly about 14 700 years ago following the Older Dryas, ended about 12 700 years ago, and was followed by the Younger Dryas. Formerly the interstadial was divided into separate Bølling and Allerød episodes, but it is now apparent that they constituted a single interstadial interrupted by several cooler episodes. Pollen records for the NW European area indicate a cool temperate flora with birch (Betula species) widespread.