a. Geol. [f. Gr. ἀρχαῖ-ος ancient + -AN.] Of or belonging to the earliest geological period.
1881. C. Fish, in Pop. Sc. Monthly, XIX. 25. The granitic or Laurentian is of archæan origin.
1882. Pall Mall Gaz., 13 Nov., 5/1. The still problematic archæan schists.
