A peculiar structure found in the Archaean limestones of Canada and other regions: According to some geologists, eozoon is believed to be a species of gigantic "Foraminifera", but others consider it a concretion, without organic structure.

"Foraminifera", which are single-celled planktonic animals with perforated chalky shells, consist of an extensive order of rhizopods which generally have chambered calcareous shells formed by several united zooids. Many of them have perforated walls, whence the name. Some species are covered with sand.