What is "chalk period"

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.

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.