The Collaborative International Dictionary of English v.0.48:

Infusorial \In`fu*so"ri*al\, 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]