Chalk n.
  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.
  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.
  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.