WALDRON, John W.F., Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G2E3, Canada, john.waldron@ualberta.ca, SCHOFIELD, D.I., British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, United Kingdom, THOMAS, C.W., British Geological Survey, Murchison House, West Mains Road, Keyworth, Edinburgh, EH93LA, Scotland, and MURPHY, J. Brendan, Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada