1. Differential weathering of volcanic ash and pumice, resulting in formation of hydrated halloysite;Aomine;Am. Min.,1962
2. Some ash showers of the central North Island;Baumgart;N.Z. Jour. Sci. and Tech. Section B,1954
3. Titanium dioxide in pyroclastic layers from volcanoes in the Cascade Range;Czamanske;Science,1965
4. Radioactive dating of tephra. Means of correlation of Quaternary successions;Damon,1968