| Answer | Crossword Clue |
|---|---|
| silurian | formed in the third period of the Palaeozoic era |
| devonian | relating to a type of rock formed in the fourth period of the Palaeozoic era |
| permian | relating to the last period of the Palaeozoic era |
| quaternary | Of, relating to, or denoting the most recent period in the Cenozoic era, following the Tertiary period and comprising the Pleistocene and Holocene epochs (and thus including the present) |
| eocene | of rock formed in the second epoch of the Tertiary geological period |
