1. Trilobites and intercontinental tie points in the Upper Cambrian of Scandinavia;Ahlberg;Geologica Acta,2003
2. Allen P.M. Jackson A.A. (1978) Bryn-teg borehole, North Wales (Bulletin of the Geological Survey of Great Britain), 61.
3. Allen P.M. Jackson A.A. (1985) Geology of the country around Harlech. Memoir of the British Geological Survey, British Geological Survey, (Keyworth, Nottingham) Sheet 135 with part of 149.
4. THE STRATIGRAPHY OF THE MAWDDACH GROUP IN THE CAMBRIAN SUCCESSION OF NORTH WALES
5. Cambrian chronostratigraphy: Current state and future plans