1. Black, L. P., Gale, N. H., Moorbath, S., Pankhurst, R. J., and McGregor, V. R., Earth Planet. Sci. Lett., 12, 245 (1971).
2. McGregor, V. R., Proc. Roy. Soc. (in the press).
3. Keto, L., Isua, a Major Iron Ore Discovery in Greenland (Kryolitselskabet Øresund A/S, Copenhagen, 1970).
4. Keto, L., Abstracts Nordic Winter Meeting (Lyngby, Denmark, 1970).
5. York, D., Earth Planet. Sci. Lett., 5, 320 (1969).