1. Dewey, J. F., and Kay, M., in History of the Crust of the Earth (Princeton Univ. Press, in the press).
2. Bullard, E. C., Everett, J. E., and Smith, A., Gilbert, Roy. Soc. Lond. Phil. Trans., No. 1088, 41 (1965).
3. Dearnely, R., Nature, 206, 1083 (1965).
4. Sutton, J., Proc. Geol. Assoc., 79, 275 (1968).
5. Wilson, J. T., Nature, 211, 676 (1966).