Published online by Cambridge University Press: 01 May 2009
There can be little doubt that most petrologists will welcome J- the classification of igneous rocks according to their grainsize as proposed by the British Association Committee on Rock Nomenclature and Classification (1). This classification has been incorporated in the new edition of the well-known textbook of Hatch and Wells (2) and has recently been very ably defended by Wells (3). To avoid misunderstanding it must be emphasized that grain-size is taken to be only one of the factors in the classification of igneous rocks and not the sole factor, and that the suggested limits between different grades of granularity must be taken at the present time to be only provisional.