1. Baldwin, R. B.: 1969,Astron. J. 74, 570.
2. Boyce, J. M. and Johnson, D.: 1977,Proc. Lunar Sci. Conf. 8, 3495.
3. Boyce, J. M., Dial, A., and Soderblom, L.: 1975, USGSInteragency Rept. Astrogeology 66, 25 pp.
4. Brett, R.: 1975,Geochim. Cosmochim. Acta 39, 1135.
5. Bryan, W. and Adams, M.: 1974,Proc. Lunar Sci. Conf. 5, 25.