1. Baldwin, R. B., “The Face of the Moon” (Univ. of Chicago Press, 1949).
2. Kuiper, G. P., Proc. U.S. Nat. Acad. Sci., 40, 1096 (1954).
3. Urey, H., “The Planets” (Yale Univ. Press, 1952).
4. Meen, V. B., J. Roy. Astro. Soc. Canada, 44, 169 (1951).
5. Karpov, R., Meteoritics, 1, 31 (1953).