| {_Permian_ {Middle, or | | | | { {Magnesian | (Earliest | | | { { Limestone. | true | | | { {Lower. | Reptiles.) | | | { | | | | { {Upper | | | | { { Coal-Formation.| | | | {_Carbon- {Coal-Formation | | | | { iferous_ {Carboniferous | | | | { { Limestone. | | | | { {Lower | | | | P { { Coal-Formation.| | | | A { | | | | L { {Upper. | Age of | Age of | | Æ {_Devonian_ {Middle. | _Amphibians_ |_Acrogens_ and| | O { {Lower. | and _Fishes_.|_Gymnosperms_.| | Z { | | (Earliest | | O {_Silurian_ {Upper. | |Land Plants.) | | I { {Lower. | | Age of | | C. { | | _Algæ_. | | {_Siluro-Cam- | Age of | | | { brian_ or {Upper. | _Mollusks_, | | | {_Ordovician_ {Lower. | _Corals_, and | | | { | _Crustaceans_.| | | { {Upper. | | | | {_Cambrian_ {Middle. | | | | {Lower | | | | | | | | --------------------------------+---------------+--------------+ | | | | | {_Huronian_ {Upper. | | | | { {Lower. | | | | E { | Age of | | | O { | _Protozoa_. | Indications | | Z { | (First animal | Plants | | O { {Upper. | remains.) | not | | I {_Laurentian_ {Middle, | |determinable. | | C. {Lower, or | | | | {Bojian. | | | | | | | +--------------------------------------+---------------+--------------+