1. Notes on the Millstone Grit of the north crop of the Pembrokeshire coalfield;Archer;Proc Geol Ass,1965
2. Archer, A. A. 1969. The Upper Carboniferous and later formations of the Gwendraeth Valley and adjoining areas. Mem. geol. Surv. U.K.
3. Zur Gliederung des Namurs im Aachener Gebiet;Bouckaert;Fortschr Geol Rheinld Westf,1960
4. Chalard, J. 1960. Contribution a l'etude de Namurien de bassin houiller du nord de la France. 2 vols. Serv. géol Houillères du Bassin du Nord et du Pas-de-Calais.
5. Unconformity-bounded stratigraphic units