1. 44 Fairpark Drive Ottawa Ontario K2G 6X8 Canada
2. Department of Earth and Planetary Sciences Yale University New Haven Connecticut 06520 USA
3. Yale Peabody Museum of Natural History Yale University New Haven Connecticut 06520 USA
4. Geology Department Pomona College Claremont California 91711 USA
5. Department of the Geophysical Sciences University of Chicago Chicago Illinois 60637 USA