The discovery of the site is attributed to geologist Jules Gosselet at the end of the 19th century. The deposit was frequently visited by paleontologists due to the profusion of fossils, the diversity of species, plus the quality of their preservation. It was subjected to intensive extraction by amateurs and professionals. The nature reserve was created in 1991 to regulate uncontrolled exploitation of the site and to allow conservation and study of fossils. Initially entrusted to the Ardennes Natural History Society. In 1996 responsibility moved to the National Forests Office. It is accessible to everyone, with a strict ban on extracting and collecting fossils and minerals. Today, the main threats are intrusion of shrub vegetation and water infiltration as shale is very brittle.
Fossil collections
These protection measures have been seen as controversial: banning collecting prevents new scientific study, despite the site's potential. Natural erosion will ultimately destroy outcropping fossils, which could be exploited without degrading the site. Few studies are funded and this "set-aside" deprives the scientific community of discoveries and collection of information that competent amateur paleontologists could make. Part of the collections are kept at the Bogny-sur-meuse Museum of fossils and minerals with the help of the Mineralogical and Paleontological Association of Bogny-sur-Meuse who have assembled the collections allowing researchers to study these fossils today. Despite the large quantity of fossils extracted from the site, knowledge of the fauna of middle Devonian remains incomplete. Many species are not yet listed or have been incorrectly named. Most has not yet been the subject of in-depth scientific study. Scientists exploit museum and other collections to better understand this fauna and more particularly the trilobites.
Geography
The reserve is located in Vireux-Molhain in the Ardennes, on the northern slope of the Viroin valley, a few kilometers from its junction with the Meuse, in the Calestienne narrow limestone strip. It marks the transition from the Ardennes to the Fagne and the Famenne. It is accessed by an embankment on the edge of “Najauge road” between Vireux-Molhain and Treignes. Collection of fossils and minerals is prohibited there.
Geology
Customs Wall is an outcrop of rocks, formation of which began in Lower Eifelian, a period of Middle Devonian. These sediments formed 397 million years ago. The sedimentary layers were subsequently folded and subjected to temperature and pressure constraints during the orogeny of the Ardennes massif. In more modern times, the Meuse and its tributaries have dug deep valleys in the plateau, revealing this outcrop of shales. Until the beginning of the century, the layers of Customs Wall were considered to belong to Assise de Bure and date from Lower Couvinian. The revision of the geological map of Givet and recent studies have shown that they belong to the Jemelle formation of Lower Eifelian.
Fossil fauna
During Lower Eifelian, about 393 million years ago, the region was submerged by a shallow sea. Life developed there in calm and warm waters. Corpses of dead animals were covered with sediment, initiating fossilization. The most abundant fossils are trilobites, but along with reef organisms and cnidarians. Identified trilobites :
