What does "greensand" mean?

Greensand: 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: Greensand is often called marl, because it is a useful fertilizer. The greensand beds of the American Cretaceous belong mostly to the Upper Cretaceous.