I have been following the correspondence in New Zealand Soil- News regarding the classification of the New Plymouth and Otorohanga series with considerable interest - all the comments and replies have been illuminating. In discussing the separation (at series level) of soils developed in andesitic tephra from those in rhyolitic tephra, Clayden et al. (1989, p. 44) ask the questions: (i) ... "can we develop quantitative definitions for each of these materials , and (2) ... "can they be consistently distinguished –in the soil profile by field techniques when weathered to form the horizons of a yellow-brown loam?" The short answer to (1) is yes; the answer to (2) could be yes, but depends on the degree of quantitativeness required and the skill of the field scientist in mineral identification.