1. Late Caradoc graptolitic faunal gradients across the Iapetus Ocean
2. A correlation of Ordovician rocks in the British Isles;Williams;Geological Society of London, Special Report,1972
3. The Přídolí Series in the Welsh Borderland and south-central Wales;White;National Museum of Wales Geological Series,1989
4. The base of the Middle Ordovician Series using graphical correlation method;Stouge;Episodes,2008
5. Rodgers J. (ed.) 1956. El Sistema Càmbrico, su palaeogeografia y el problema de su base. Parts I and II. International Geological Congress, XX Session, Mexico, 1956.