1. J. Otterman and F. E. Bronner , Science 153 , 56 ( 1966 ).
2. G. Beskow The Swedish Geological Society 26th Year Book No. 3 (Swedish Road Institute Stockholm 1935; translation published by the Technological Institute Northwestern University Evanston 1947).
3. Z. A. Nersesova and N. A. Tsytovich Proceedings International Conference on Permafrost (National Academy of Sciences-National Research Council Publ. No. 1287 Washington D.C. 1963).
4. The curves in Fig. 1 were calculated from the data of Nersesova and Tsytovich; specific surfaces of 800 mF/g and 50 mV/g for montmoriilonite and kaolinite respectively were assumed.
5. P. Hoekstra and E. Chamberlain , Nature 203 , 1406 ( 1964 ).