Torrance (1983) has recently reviewed factors producing high sensitivity in clayey sediments and proposed a general model for quick clay development. He suggested that the mineralogical requirement for quick clay behaviour to develop is that low activity minerals must predominate in the sediment. This is also the essential mineralogical requirement of the inactive-particle, short-range-bond hypothesis of high sensitivity (Smalley, 1971, 1972a, 1976; Cabrera & Smalley 1973; Smalley, Ross & Whitton, 1980). The predominance of low activity minerals causes most of the interparticle bonds to be of the short-range variety which allow/promote the‘quick’ behaviour—the transition from solid to liquid. In Canadian or Scandinavian quick clays the short-range bond requirement is largely met by the abundance of finegrained primary mineral particles. The very sensitive clays involved in the Tauranga landslide in New Zealand (Smalley et al., 1980) owed their sensitivities to their content of inactive spheroidal halloysite particles. By many definitions the Tauranga material is a quick clay and its existence provides us with another window through which to view the quick clay problem. Torrance observed that for a quick clay to develop the sediment must have an open structure with a high void ratio. In a classic Canadian quick clay this structure is obtained by the slow sedimentation of fine particles in the salty Champlain Sea; in the Tauranga soil an open structure is obtained by air-fall sedimentation of the initial volcanic particles.