- GeoRef, Copyright 2004, American Geological Institute.
The I.U.G.S. Subcommission on Carboniferous Stratigraphy recommends the base of the Westphalian D be recognized using plant macrofossils. In Britain, however, South Wales is the only coalfield where the distribution of the plants is sufficiently well known for them to be used to locate this boundary. Elsewhere in Britain other criteria have been used, particularly non-marine bivalves and plant microfossils, but these must be used with considerable caution.--Modified journal abstract.