lowermost of the two standard worldwide divisions of Middle Devonian (Devonian Period) rocks and time. Eifelian time spans the interval between 397.5 million and 391.8 million years ago. The name of the Eifelian Stage is derived from the Eifel Hills in western Germany, near Luxembourg and Belgium. As formally ratified in 1985 under the authority of the International Commission on Stratigraphy, the Global Stratotype Section and Point (GSSP) defining the lower boundary of this stage is established in a trench section across pastureland near the town of Schönecken-Wetteldorf, Ger. The trench exposes siltstones and mudstones in the upper part of the Heisdorf Formation and alternating limestones and mudstones in overlying strata of the Lauch Formation. The boundary point is situated 1.9 metres (6.2 feet) below the base of the Lauch Formation, which is fixed by the first occurrence of the conodont Polygnathus costatus partitus, known worldwide from Eifelian strata in Morocco, Spain, Germany, Austria, the Czech Republic, Central Asia, China, Malaysia, Australia, the U.S. states of Nevada and Alaska, and the Canadian Arctic. The top of the Eifelian Stage is defined by the base of an overlying subdivision, the Givetian Stage of the Middle Devonian Series, while the bottom is underlain by the Emsian Stage of the Lower Devonian Series.