The Collaborative International Dictionary of English v.0.48:

Cretacic \Cre*tac"ic\
   [Webster 1913 Suppl. +PJC]

   Cretaceous acid,
   an old name for carbonic acid.

   Cretaceous formation (Geol.), the series of strata of
      various kinds, including beds of chalk, green sand, etc.,
      formed in the Cretaceous period; -- called also the chalk
      formation. See the Diagram under Geology.

   Cretaceous period (Geol.), the time in the latter part of
      the Mesozoic age during which the Cretaceous formation was
      deposited, and at the end of which the dinosaurs died out.
      See Cretaceous.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Chalk \Chalk\ (ch[add]k), n. [AS. cealc lime, from L. calx
   limestone. See Calz, and Cawk.]
   1. (Min.) A soft, earthy substance, of a white, grayish, or
      yellowish white color, consisting of calcium carbonate,
      and having the same composition as common limestone.
      [1913 Webster]

   2. (Fine Arts) Finely prepared chalk, used as a drawing
      implement; also, by extension, a compound, as of clay and
      black lead, or the like, used in the same manner. See
      Crayon.
      [1913 Webster]

   Black chalk, a mineral of a bluish color, of a slaty
      texture, and soiling the fingers when handled; a variety
      of argillaceous slate.

   By a long chalk, by a long way; by many degrees. [Slang]
      --Lowell.

   Chalk drawing (Fine Arts), a drawing made with crayons. See
      Crayon.

   Chalk formation. See Cretaceous formation, under
      Cretaceous.

   Chalk line, a cord rubbed with chalk, used for making
      straight lines on boards or other material, as a guide in
      cutting or in arranging work.

   Chalk mixture, a preparation of chalk, cinnamon, and sugar
      in gum water, much used in diarrheal affection, esp. of
      infants.

   Chalk period. (Geol.) See Cretaceous period, under
      Cretaceous.

   Chalk pit, a pit in which chalk is dug.

   Drawing chalk. See Crayon, n., 1.

   French chalk, steatite or soapstone, a soft magnesian
      mineral.

   Red chalk, an indurated clayey ocher containing iron, and
      used by painters and artificers; reddle.
      [1913 Webster]