Source : Webster's Revised Unabridged Dictionary (1913)

Laurentian \Lau*ren"tian\, a.
   Pertaining to, or near, the St. Lawrence River; as, the
   Laurentian hills.

   {Laurentian period} (Geol.), the lower of the two divisions
      of the Arch[ae]an age; -- called also {the Laurentian}.