*greensan*

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. [ 1913 Webster ]

☞Greensand is often called marl, because it is a useful fertilizer. The greensand beds of the American Cretaceous belong mostly to the Upper Cretaceous. [ 1913 Webster ]