1. University College London
Gower Street, London WC1E 6BT, UK
rob@gl.rhul.ac.uk
2. Institute of Geological Sciences, Polish Academy of Sciences, Kraków Research Centre
ul. Senacka 1, 30-001 Kraków, Poland
3. Department of Geology, Royal Holloway, University of London
Egham, Surrey, TW20 0EX, UK