1. Bowers, R., J. Brit. I.R.E., 25, No. 5, 457 (1963).
2. Clarke, A. M., Chambers, R. E., Allonby, R. H., and Magraw, D., Min. Eng., No. 15, 197 (1961).
3. Magraw, D., Clarke, A. M., and Smith, D. B., Proc. Yorks. Geol. Soc., 34, No. 2, 153 (1963).
4. Downing, R. A., Geol. Mag., 96, 81 (1959).
5. Donovan, D. T., Ann. Rep. Challenger Soc. for 1964–5 (in the press).