1964 master's thesis by P.E.H. Gregg at University of Canterbury

scholarly article

scientific article published in October 1988

scientific article published in January 1990

1976 doctoral thesis by P. E. H. Gregg at University of Canterbury

scientific article published in 1990

article

scholarly article by B.H. Robinson et al published January 1999 in Geoderma

scholarly article by B.H. Robinson et al published December 1997 in Journal of Geochemical Exploration

scientific article published in July 1989

scientific article published in July 1990