the lower stage of the Middle Devonian system (period). The Eifelian was established in the Eifel Mountains (in what is now the Federal Republic of Germany) in 1848 by the Belgian geologist A. Dumont. The stratotype of the Eifelian is represented chiefly by marls. In the Ardennes of Belgium it corresponds approximately to the shales of the Couvinian stage of J. d’Omalius d’Halloi, whose base is stratigraphically lower than the base of the Eifelian.
In the USSR the Eifelian (Couvinian) is taken to be more inclusive than in the stratotype and includes the analogues of the Zlihovian stage of Czechoslovakia and the upper part of the Em-sian stage of the Rhine region. The Eifelian, which is divided into two substages, is widespread and represented by various rocks, such as marine carbonate and terrigenous rocks, evaporites, continental detrital rocks, and effusive rocks. In the USSR, complex ores, bauxites, iron, manganese, titanium, petroleum, rock salt, and other mineral products are associated with Eifelian beds.