The geology of the town comprises bedrock formed in the Coniacian, Santonian and Campanian ages of the Late Cretaceous epoch, overlain in places by more recent Quaternary drift deposits. The bedrock is chalk of various formations. The drift deposits comprise a cap of clay-with-flints on the western edge of the town around Poundbury, alluvium in the river's floodplain, and several narrow ribbons of poorly stratified head deposits, found particularly around the town's northeastern and southwestern boundaries but also elsewhere.[54]