{ VI. Permian { 14. _Zechstein_ | Upper Permian II. _Primary { { 13. | Lower Permian Group_, { { 12. _Carboniferous | or { V. Carbonic sandstone_ | Upper carbonic Palæolithic { (coal) { 11. _Carboniferous | (Palæozoic) { { limestone_ | Lower carbonic groups of { IV. Devonian { 10. _Pilton_ | Upper Devonian strata {(Old red sandstone){ 9. _Ilfracombe_ | Mid Devonian { 8. _Linton_ | Lower Devonian I. _Primordial { { 7. _Ludlow_ | Upper Silurian Group_, { III. Silurian { 6. _Llandovery_ | Mid Silurian or { { 5. _Llandeilo_ | Lower Silurian Archilithic { (Archizoic) { II. Cambrian { 4. _Potsdam_ | Upper Cambrian groups of { { 3. _Longmynd_ | Lower Cambrian strata { { I. Laurentian { 2. _Labrador_ | Upper Laurentian { { 1. _Ottawa_ | Lower Laurentian The fourth main division of the organic history of the earth, the _tertiary epoch_, or _era of Leafed Forests_, is much shorter and less peculiar than the three first epochs. This epoch, which is also called the cænolithic or cænozoic epoch, extended from the end of the cretaceous system to the end of the pliocene system. The strata deposited during it amount only to a thickness of about 3000 feet, and consequently are much inferior to the three first great groups. The three systems also into which the tertiary period is subdivided are very difficult to distinguish from one another. The oldest of them is called _eocene_, or old tertiary; the newer _miocene_, or mid tertiary; and the last is the _pliocene_, or later tertiary system.