11. The ground is mostly composed of Tertiary period rocks known for producing high-quality clay. 12. During the ensuing Tertiary period of the Cenozoic era, sea levels also varied substantially. 13. Luray Caverns does not date beyond the Tertiary period . 14. The Leipzig Bay was formed during the Tertiary period . 15. During most of the Tertiary period of the Cenozoic southern Alabama was covered by the sea. 16. Instead, the most marked erosion took place during the Tertiary period , entirely under a tropical climate. 17. The survivors speciated rapidly during the Tertiary period . 18. The ensuing Tertiary period of the Cenozoic era is also missing from the local rock record. 19. In 1828, Charles Lyell incorporated a Tertiary Period into his own, far more detailed system of classification. 20. This gap in the rock record continues into the Cenozoic era and spans the entire Tertiary period .