The Geological Period
1. Cambrian
2. Ordovician
3. Silurian
4. Devonian
5. Carboniferous (sometimes split into Mississippian/Pennsylvanian)
6. Permian
7. Triassic
8. Jurassic
9. Cretaceous
10. Paleogene (often referred to as Tertiary in older texts)
11. Neogene (also formerly part of Tertiary)
12. Quaternary
