ASHGILL SERIES

also called Ashgillian Series, the uppermost (in ascending order) of six divisions constituting the Ordovician System, representing all those rocks deposited worldwide during the Ashgillian Age (448 to 438 million years ago). The name of the series is derived from the Ash Gill Slates in the vicinity of Coniston in the Lake District of Cumbria, Eng., which is the type area for rocks of this age. Cautley, also in Cumbria, is another type area for Ashgill rocks. About 155 m (500 feet) of Ashgill rock strata occur in South Wales; all are sedimentary, in contrast to Lower Ordovician rocks, which contain extensive volcanic deposits. No global stratotype section and point (GSSP) for the Ashgill has yet been defined by the International Commission on Stratigraphy. The base of the fossil zone of the graptolite Dicellograptus complanatus occurs just above the base of Ashgill strata in the Lake District and is a possible defining point for the series. The fossil zone of the conodont Amorphognathus ordovicicus is also found in the series. The top of the Ashgill Series is well defined by the base of the overlying Llandovery Series, which forms the base of the Silurian System.