Source : Webster's Revised Unabridged Dictionary (1913)

Infusorial \In`fu*so"ri*al\, a. (Zo["o]l.)
   Belonging to the Infusoria; composed of, or containing,
   Infusoria; as, infusorial earth.

   {Infusorial earth} (Geol.), a deposit of fine, usually white,
      siliceous material, composed mainly of the shells of the
      microscopic plants called diatoms. It is used in polishing
      powder, and in the manufacture of dynamite.