[Illustration] [Illustration: +------------------------------------------------------------------+ | IDEAL SECTION OF EARTH’S CRUST | | | | ERAS AGES PERIODS STRATA | +---------+-------------+----------------+-----------------+-------+ | | | |TERRACE | | |BYCHOZOIC|MAN |QUATERNARY |CHAMPLAIN | | | | | |GLACIAL | | +---------+-------------+----------------+-----------------+-------+ | | | |PLIOCENE | | |CENOZOIC |MAMMALS |TERTIARY |MIOCENE | | | | | |EOCENE | | +---------+-------------+----------------+-----------------+-------+ | |BIRDS |CRETACEOUS | | | | +-------------+----------------+-----------------+-------+ | | |JURASSIC | | | | |REPTILES +----------------+-----------------+-------+ | | |TRIASSIC | | | |MESOZOIC | +----------------+-----------------+-------+ | |ACROGENS | |PERMIAN | | | |AMPHIBIANS |CARBONIFEROUS |CARBONIFEROUS | | | | | |SUB-CARBONIFEROUS| | | +-------------+----------------+-----------------+-------+ | |FISHES |DEVONIAN |CATSKILL, CHEMUNG| | | | | |CORNIFEROUS, Etc.| | | +-------------+----------------+-----------------+-------+ | | |SILURIAN |LOW HELDERBERG | | |PALEOZOIC| | | NIAGARA | | | | +----------------+-----------------+-------+ | |INVERTEBRATES|ORDOVICIAN |LORRAINE, TRENTON| | | | | | CHAZY | | | | +----------------+-----------------+-------+ | | |CAMBRIAN |POTSDAM, ACADIAN | | | | | | GEORGIA | | | +-------------+----------------+-----------------+-------+ | | | |KENESAW | | | | |ALGONKIAN |HURONIAN, Etc. | | |EOZOIC +-------------+----------------+-----------------+-------+ | | |ARCHAEAN |LAURENTIAN, Etc. | | +---------+-------------+----------------+-----------------+-------+ | AZOIC ERA | |