Algonkian

Al*gon"ki*an, a.

1. Var. of Algonquian.

2. (Geol.) Pertaining to or designating a period or era recognized by the United States Geological Survey and some other authorities, between the Archæan and the Paleozoic, from both of which it is generally separated in the record by unconformities. Algonkian rocks are both sedimentary and igneous. Although fossils are rare, life certainly existed in this period. -- n.

Defn: The Algonkian period or era, or system or group of systems.