- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
The lithological and faunal changes through the transition from non-marine Hangman grits to marine Ilfracombe beds of north Devon and west Somerset suggest the presence of a major depositional marine transgression. A fauna of thick-shelled lamellibranchs and gastropods occurs in beds lying stratigraphically between the fluviatile Hangman deposits below, and the shallow-water marine Ilfracombe beds above, and is considered to indicate an intermediate phase of intertidal depositional conditions. The transgression appears to have advanced across the region in a north-north-easterly direction during lower-middle Givetian times following coastal subsidence and possibly an associated rise of sea level.