a. (Zool.) Belonging to the Infusoria; composed of, or containing, Infusoria; as, infusorial earth. [ 1913 Webster ]

Infusorial earth (Geol.), a deposit of fine, usually white, siliceous material, composed mainly of the shells of the microscopic plants called diatoms; also called diatomaceous earth, kieselguhr, and diatomite. It is used in polishing powder, and in the manufacture of dynamite. [ 1913 Webster +PJC ]