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Summary Petrography of the acid igneous rock of the Shag Valley in North‐east Otago, previously classified as a quartz porphyry, indicates that this rock is an ignimbrite. Formerly described as a dyke, the Shag Valley rock is now considered to be a surface rock interbedded with coal measures of Upper Senonian age, and is the first occurrence of ignimbrite described from the South Tsland of New Zealand.
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Steiner et al. (1959) studied this question.
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