1. Coode, A. M., unpublished thesis, Univ. British Columbia (1963).
2. Coode, A. M., and Tozer, D. C., Nature, 205, 164 (1965).
3. Schmucker, U., Geomag. and Geoelect., 15, 193 (1964).
4. Hyndman, R. D., unpublished thesis, Univ. British Columbia (1963).
5. Lambert, A., and Caner, B., Can. J. Earth Sci., 2 (to be published).