The Paleogene and Neogene are sometimes referred to as the Tertiary Period. Almost all of the Paleogene and Neogene sediments occur in the Jackson Purchase Region in extreme western Kentucky and most have not been consolidated (cemented) into rocks. Most of these sediments are shales, clay, or sands that were deposited in coastal or river and floodplain environments. The most common fossils are coalified limbs, logs, and stumps of lignite rank. Some beautifully preserved tree leaves have been found. The potential exists for a variety of mammal fossils to be found in these sediments in Kentucky, but a great deal of new research needs to be done on these sediments. Some of the mammal fossils found in Kentucky may have come from the Pliocene Series, the last series of the Neogene.