The Darent is a Kentish tributary of the River Thames and takes the waters of the River Cray as a tributary in the tidal portion of the Darent near Crayford, as illustrated by the adjacent photograph, snapped at high tide. 'Darenth' is frequently found in the spelling of the river's name in older books and maps, Bartholomew's "Canal's and River of England" being one example. Bartholomew's Gazetteer (1954) demonstrates that "Darent" means "clear water" and separately explains the other name. Considering the River Darent runs on a bed of chalk and its springs rise through chalk, this is not surprising. The original purity of the water was a major reason for the development of paper and pharmaceuticals in the area.