The Upper Jurassic (140 million years ago) "lithographic" limestone from quarries at this site are extremely fine-grained and as such allow the preservation of very fine detail in fossil impressions. Fossil insects such as the drogonfly Libellulium complete with impressions of their delicate wings have been discovered. It is here that the first fossils of archaeopteryx - the oldest bird - were found, showing feathers as well as classic reptilian characteristics. These fossils have since been used as the basis that all birds today evolved from small dinosaurs.
Marine fossils are also found in the Kimmeridgian strata at this location, such as the "Horse-shoe" crab Mesolimulus, the stemless crinoid Pterocoma and herring-like fish Leptolepis.