Michael Bassett is keeper of Geology at the National Museum of Wales and an Honorary Professor in Geology at the University of Wales Cardiff. His research studies in paleontology and stratigraphy have been published in over 100 scientific articles amd books, and he is editor of Geological Excursions in Dyfed: South-west Wales and Siberian Field Excursions: A Geotraverse Across Wales and the Welsh Borderland. Nigel Woodcock is a lecturer in the Department of Earth Sciences at the University of Cambridge and a Fellow of Clare College. He is the author of over eighty scientific publications, specializing in structural geology, sedimentology and environmental geology. With postgraduate students he has made extensive contributions to current understanding of the Palaeozoic rocks of Wales.