Spilitic rocks from several localities in the northern part of North Island, New Zealand, where they occur associated with keratophyres and interbedded graywackes, have been studied chemically and petrogenetically. These spilites are particularly interesting because, unlike many examples, they are apparently unmetamorphosed. Close affinity to tholeiites is exhibited in many respects (texture, differentiation trend, and others), and there seems no need to postulate a special primary magma. Water as a component of the magma and the retention of the volatile oxides are considered in their effect on mineral crystallization and the development of the spilitic series.

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