allogenic valley

   A karst valley incised by a watercourse originating on impervious rock with a volume sufficient for it to traverse a limestone area on the surface.

   The valley is incised from the limestone contact and with the passage of time the river is increasingly likely to pass underground as the waters enlarge joints. Occasionally such a valley may represent the large-scale collapse of the cavern system along a subterranean stream or the enlarging of a series of karst windows [19].