1. P. R. Bierman, Department of Geology, University of Vermont, Burlington, VT 05405, USA.
2. A. R. Gillespie, Department of Geological Sciences, University of Washington, Seattle, WA 98195, USA.
3. M. W. Caffee, Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.