(Geol.) Pertaining to or designating a period or era recognized by the United States Geological Survey and some other authorities, between the Archaean 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.
noun
Algonkian n. The Algonkian period or era, or system or group of systems.
... Algonkin, meaning an Indian, is also spelled Algonquin. But the adjective from this noun is spelled Algonquian when applied to Indians, and Algonkian when applied to a time or ... — Boys' Book of Indian Warriors - and Heroic Indian Women • Edwin L. Sabin
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