1. Department of Geology, University of LeicesterLeicester LE1 7RH, UK
2. Geological Collections, University Museum of Natural HistoryOxford OX1 3PW, UK
3. Department of Earth Sciences, University of OxfordParks Road, Oxford OX1 3PR, UK
4. Department of Earth Sciences and Engineering, Imperial College LondonLondon SW7 2BP, UK
5. Department of Geology & Geophysics, Yale UniversityPO Box 208109, New Haven, CT 06520-8109, USA