1. Hills, I. R., and Whitehead, E. V., Nature, 209, 977 (1966).
2. Hills, I. R., and Whitehead, E. V., Proc. Third Intern. Meeting on Geochem., London, September, 1966 (in the press).
3. Louis, M., CR Acad. Sci., 256, 5610 (1963).
4. Louis, M., Rev. Inst. Franç. Pétrole, 19, 277 (1964).
5. Budzikiewicz, H., Wilson, J. M., and Djerassi, K., J. Amer. Chem. Soc., 85, 3688 (1963).