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.

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