At the end of the Mesozoic and at the beginning of the Paleogene the Bükk mountain became a land and after it became a land in the Bükk Mountains. With the help of land degradation, younger Mesozoic sediments have been destroyed, in many places a Triassic limestone can be reached. Only in a late Eocene did it once again be covered with sea and finish. The sea flooding lasted until the end of the Oligocene, but the whole area of the montain has never been flooded entirely. In the upper Eocene, after some 40 million years, the Szépvölgy Limestone Formation was formed under shallow sea conditions. They formed on Triassic limestone bedrock. Its main mass is composed of light gray-yellow, often tubular, limestone, with thinner or thicker layers of marl at the center of the benches. Characteristically rich in biogenic limestone, which is dominated by Lithotamniums (red algae) and single-celled largeforaminifera (Nummulitea) The Szépvölgyi Limestone formation, based on its development and its ancient remains, it was formed in the shallow marine environment. It can be observed on the south side of the Nagy-Eged and on the Kis-Eged. At the end of the Eocene, the sea began to deepen. At the foot of the mountain, the Lower Oligocene Buda Marl Formation is deposited in the Eocene limestone cover. The boundaries of the Szépvölgy Limestone and the Buda Marl in the Bükk Mountains coincide with the boundaries of the Eocene and Oligocene ages. Only from the Southern Bükk is known as the Tardi Clay Formation emerging from the Buda marl. One of its most important excavations can be found in Kis-Eged. Its middle level is a light gray clay aleurit with only a rich mussel fauna on the Little Eged. Fish and leaf remains are common in the often leavened upper level. According to the leaves fossils, the area may have been a mangrove forest formed in a tropical environment.
