Cambrian period.
Ordovician period.
Silurian period.
Devonian period.
Mississippian period.
Pennsylvanian period.
Permian period.
Mesozoic era. (Reptiles.)
Triassic period.
Jurassic period.
Comanchean period.
Cretaceous period.
Cenozoic era. (Mammals.)
Oligocene and Eocene time
Pliocene and Miocene time.
Pleistocene time.