1. Arrhenius, G., Liang, S., MacDougall, D., Wilkening, L., Bhandari, N., Bhat, S., Lal, D., Rajagopalan, G., Tamhane, A. S., and Venkatavaradan, V. S.: 1971,Proc. Second Lunar Sci. Conf. 3, 2583.
2. Barber, D. J., Hutcheon, I., and Price, P. B.: 1971,Science 171, 372.
3. Borg, J., Maurette, M., Durrieu, L., and Jouret, C.: 1971,Proc. Second Lunar Sci. Conf. 3, 2027.
4. Comstock, G. M.: 1971, in H. C. Urey and S. K. Runcorn (eds.), ?The Moon?,IAU Symp. 47, 330.
5. Comstock, G. M., Evwaraye, A. O., Fleischer, R. L., and Hart, H. R., Jr.: 1971,Proc. Second Lunar Sci. Conf. 3, 2569.