Paleontology and geology
The Tertiary was a time of increased stream deposition with the accumulation of conglomerates, sandstone, and clay in the Jackson Purchase area of western Kentucky. The clay deposits contain abundant plant fossils, including leaves and wood that eventually changed to lignite, a brownish black coal. Tertiary sediments in the rest of Kentucky consist of stream gravels and other sediments that cap the hills in Central Kentucky and other regions. These gravels contain microfossils, including plant pollen.