\Green"sand`\ (-s?nd`), n. (Geol.)
A variety of sandstone, usually imperfectly consolidated,
consisting largely of glauconite, a silicate of iron and
potash of a green color, mixed with sand and a trace of
phosphate of lime.
Note: [hand]Greensand is often called {marl}, because it is a
      useful fertilizer. The greensand beds of the American
      Cretaceous belong mostly to the Upper Cretaceous.