Era
Cretaceous
19
Permian
9
Tertiary
9
Cenozoic
8
Pennsylvanian
7
Quaternary
7
Jurassic
5
Mississippian
5
Paleozoic
5
Triassic
5
Cambrian
4
Eocene
4
Miocene
3
Ordovician
3
Pleistocene
3
Carboniferous
2
Neogene
2
Oligocene
2
Paleocene
2
Paleogene
2
Pre-Quaternary
2
Precambrian
2
1844-1909
1
Devonian
1
Holocene
1
Mesozoic
1
Pliocene
1