1. Nicholas, T. C., Quart. J. Geol. Soc., 71, 83 (1915).
2. Kopstein, F. P. H. W., Ph.D. thesis, Univ. Groningen (1954).
3. Bassett, D. A., and Walton, E. K., Quart. J. Geol. Soc., 116, 95 (1959).
4. Matley, C. A., and Wilson, T. S., Quart. J. Geol. Soc., 102, 1 (1946).
5. Knill, J. L., J. Sediment. Petrol., 29, 317 (1959).