Abstract
Abstract Deposits of Lower Eocene low-grade swelling bentonite of marine origin are widespread in North Canterbury. Large deposits of non-swelling bentonite, of Miocene age and probably formed by the alteration of glassy basalt ash deposited in a freshwater lake, occur in the Harper Hills, 40 miles west of Christchurch. The essential mineral is an iron-rich montmorillonite containing a minor, interlay er ed, non-expanding component and having about 100meq/100g cation exchange capacity saturated with calcium and magnesium ions. The bentonite can be converted to a high-grade swelling form by treatment with sodium carbonate.
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