agnotozoic

from The Century Dictionary.

• Not known to contain fossils: applied to the early rocks and period of the earth in which definite evidence of organic life has not been found.
• noun The rocks and period not yet known to contain evidences of life: contrasted with eozoic and paleozoic, and essentially equivalent, so far as the term has been applied, to the Huronian of Logan and the Algonkian of Walcott. Not in general use.