1. Department of Geology and Environmental Earth Science, Miami University, 118 Shideler Hall, 250 S. Patterson Avenue, Oxford, Ohio 45056, USA
2. Geology Department, Juniata College, 1700 Moore Street, Huntingdon, Pennsylvania 16652, USA
3. Space Sciences Laboratory, University of California at Berkeley, 7 Gauss Way, Berkeley, California 94720, USA