Webster’s Revised Unabridged Dictionary · 1913
Argillaceous
Ar′gil·la′ceous, a. [L. argillaceus, fr. argilla.] Of the nature of clay; consisting of, or containing, argil or clay; clayey.
Argillaceous sandstone (Geol.), a sandstone containing much clay. — Argillaceous iron ore, the clay ironstone. — Argillaceous schist or state. See Argillite.