Bourne, Hailbourne, or Winterbourne, an intermittent spring or stream, occurring commonly in chalk districts after an exceptionally wet season. They owe their origin to a general rise of water underground throughout the area, flowing out at all points where the level of the surface of the ground is lower than the level to which the underground water rises (saturation-plane). They therefore often flow along those "dry valleys" of our chalk downs which were probably permanent watercourses in a more pluvial period. They rise at Hemel Hempstead and Henley in the Chiltern Hills, at Croydon, Caterham, Merstham and Epsom in the North Downs, at Ashcombe near Lewes, and at Lavant in the South Downs, and also in Wiltshire and Dorsetshire. From the time of Werkworth in the 15th century, and the credulous John Aubrey in the 17th, to our own time, the outbreak of these bournes has been popularly supposed to foreshadow national misfortune.