+----------------------------------------------------+ | Post Tertiary.| | +----------------------------------------------------+ Tertiary. {| Pliocene. | | +----------------------------------------------------+ {| Miocene. | | +----------------------------------------------------+ {| Eocene. | | +----------------------------------------------------+ Secondary. {| Chalk. | Dicotyledons (Apetalæ, Polypetalæ, | {| |  Sympetalæ). | +----------------------------------------------------+ {| Oolite. | | +----------------------------------------------------+ {| Trias. | | +----------------------------------------------------+ | | | {| Permian. | | +----------------------------------------------------+ {| Carboniferous.| Monocotyledons. | +----------------------------------------------------+ {| | | {| Devonian, or | Clubmosses, Horsetails, Ferns, | {| Old Red | Gymnosperms. | {| Sandstone. | | +----------------------------------------------------+ Primary. {| Silurian. | } Cellular Cryptogams. | {| Cambrian. | } | +----------------------------------------------------+ {| Huronian. | } Indications of Plants, | {| Laurentian. | } not determinable. | +===================+================================+ | AZOIC. | | phylogenetic [or racial] evolution become the creed of some leading naturalists that they unwittingly proceed in this manifestly unphilosophical method. But it is a first axiom, though one often forgotten, in this as in every scientific enquiry, that no step can be made in advance which is not based on fact. After this initial stage, the story becomes much clearer, and at the same time less easy to reconcile with evolutionary requirements.