| Answer | Crossword Clue |
|---|---|
| oligocene | The Oligocene epoch or the system of rocks deposited during it |
| paleocene | The Paleocene epoch or the system of rocks deposited during it |
| paleozoic | The Paleozoic era or the system of rocks deposited during it |
| carboniferous | The Carboniferous period or the system of rocks deposited during it |
| tertiaries | The Tertiary period or the system of rocks deposited during it |
| triassic | The Triassic period or the system of rocks deposited during it |
