Cryptozoic Eon

synonym for Precambrian. The term was suggested by the American geologist G. Chadwick in 1930 for the largest subdivision of the geochronologic scale, during which the Precambrian rock strata which do not have visible fossils of skeletal fauna formed. The Cryptozoic eon is contrasted with the Phanerozoic eon, in whose deposits these fossils are found in large numbers.