1. Curtis, R., Evans, G., Kinsman, D. J. J., and Shearman, D. J., Nature, 197, 679 (1963).
2. Evans, G., and Shearman, D. J., Nature, 202, 385 (1964).
3. Holm, D. A., Science, 132, 1369 (1960).
4. Gould, H. R., and McFarlan, jun., E., Gulf Coast Assoc. Geol. Soc. Trans. ninth Ann. Meeting Houston, Texas, 9, 261 (1959).
5. Evans, G., Quart. J. Geol. Soc. (in the press).