STRUCTURE AND LIFE HISTORIES 
the following table, the older rocks being at the bottom, 
the most recently formed at the top. 
TABLE VI. TABLE OF GEOLOGICAL TIME 
Era Period 
Holocene 
(recent, or the present) 
Pleistocene 
(ice age) 
Cenozoic 
Mesozoic 
Quaternary 
Tertiary 
Secondary 
Paleozoic 
Primary 
Archean 
Pliocene 
Miocene 
Oligocene 
Eocene 
Upper Cretaceous 
Lower Cretaceous 
(Comanchean) 
Jurassic 
Triassic 
Permian 
Upper Carboniferous 
(Pennsylvanian) 
Lower Carboniferous 
(Mississippian) 
Devonian 
Silurian 
Ordovician 
Cambrian 
Huronian 
Laurentian 
509. Paleogeography. By changes in the relative 
level of the land and sea, above referred to, rocks contain- 
ing fossils may be elevated as dry land, and frequently 
as mountains, so that remains of marine organisms, as 
well as of others, are often found at high elevations. In 
some cases forests near the seashore have been submerged, 
