Within the Green River Formation of southwest Wyoming in the area known as Fossil Lake, two distinct zones of very fine-grained lime muds are particularly noted for preserving a variety of complete and detailed fossils. These layers are an Eocene Lagerstätte, a rare place where conditions were right for a rich accumulation of undisturbed fossils. The most productive zone—called the split fish layer—consists of a series of laminated or varved lime muds about 6 ft (1.8 m) thick, which contains abundant fish and other fossils.
Watching the preparation of these fossils is an incredible thing, first the delicate splitting of the slab and then the fine detailed scraping to reveal the detailed outline of the fossil fish, the detail can be so preserved and perfect that the fish can look painted on. Undoubtedly in some circles this can happen but rest assured we only stock the genuine article.