Laurentian period

from The Collaborative International Dictionary of English v.0.48

Laurentian \Lau*ren"tian\, a.
   Pertaining to, or near, the St. Lawrence River; as, the
   Laurentian hills.
   [1913 Webster]

   {Laurentian period} (Geol.), the lower of the two divisions
      of the Arch[ae]an age; -- called also {the Laurentian}.
      [1913 Webster]